Environmental Permit Variation Application

Slough Heat and Power Station Application Supporting Document

Slough Heat and Power Limited

Project reference: 60578218 Project number: 60578218.005 60578218-ACM-PM-RP-EN-001-A

14 April 2020

Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Quality information

Prepared by Checked by Verified by Approved by Aakanksha Sinha Helen Watson Mark Webb Mark Webb Principal Consultant Associate Director Technical Director Technical Director

Revision History

Revision Revision date Details Authorized Name Position Initial draft 10/03/2020 Client review Helen Watson Helen Watson Project Manager Final 14/04/2020 Issue Helen Watson Helen Watson Project Manager

Prepared for: Slough Heat and Power Limited AECOM Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Prepared for: Slough Heat and Power Limited Andrew Ellis 342 Edinburgh Avenue Slough SL1 4TU

Prepared by: Aakanksha Sinha Principal Consultant T: +441133012442 E: [email protected]

AECOM Infrastructure & Environment UK Limited 5th Floor, 2 City Walk Leeds LS11 9AR United Kingdom

T: +44 (0)113 391 6800 aecom.com

© 2020 AECOM Infrastructure & Environment UK Limited. All Rights Reserved.

This document has been prepared by AECOM Infrastructure & Environment UK Limited (“AECOM”) for sole use of our client (the “Client”) in accordance with generally accepted consultancy principles, the budget for fees and the terms of reference agreed between AECOM and the Client. Any information provided by third parties and referred to herein has not been checked or verified by AECOM, unless otherwise expressly stated in the document. No third party may rely upon this document without the prior and express written agreement of AECOM.

Prepared for: Slough Heat and Power Limited AECOM Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Table of Contents

Non - Technical Summary ...... 1 Introduction...... 4 2.1 Background ...... 4 2.2 Proposed Variation ...... 5 2.3 Environmental Setting ...... 6 Site Condition ...... 6 Operating Techniques ...... 7 4.1 Technical Standards ...... 7 4.2 Process Description ...... 7 4.3 Raw Materials ...... 9 4.4 Waste ...... 9 4.5 Energy Use ...... 10 4.6 Operating and Maintenance Procedures ...... 11 4.7 Management Systems ...... 11 4.8 General Maintenance ...... 11 Emissions to Air, Water and Land ...... 11 5.1 Emissions to Air ...... 11 5.2 Emissions to Water ...... 13 5.3 Emissions to Sewer ...... 14 5.4 Emissions to Land...... 14 5.5 Odour ...... 14 5.6 Noise ...... 14 5.7 Heat...... 14 Monitoring ...... 15 6.1 Infrastructure ...... 15 6.2 Emissions to Air ...... 15 6.3 Emissions to Sewer ...... 15 6.4 Emissions to Water ...... 15 6.5 Monitoring of Process Variables ...... 15 Environmental Risk Assessment (Impact Assessment) ...... 15 7.1 Introduction ...... 15 7.2 Site Location and Sensitive Receptors ...... 16 7.3 Impact Assessment ...... 18 7.4 Site Waste ...... 20 7.5 Global Warming Potential (GWP) ...... 21 7.6 Abnormal Operations ...... 21 Closure and Decommissioning ...... 21 Appendix A - Figures...... Appendix B – Air Quality Impact Assessment ...... Appendix C – List of Company Directors ...... Appendix D – Application Checklist ......

Tables

Table 4-1: Key Residue Streams from the Multifuel Facility ...... 9 Table 5-1: Point Source Releases to Air from the Installation ...... 11 Table 5-2: South Stack at Operational Design Load (10.5MJ/kg) ...... 12 Table 5-3: Emission Limit Values for the South Stack ...... 12 Table 7-1: Human Receptors in the Vicinity of the Installation ...... 16 Table 7-2: Designated European Ecological Receptors in the Vicinity of the Site (within 10 km) ...... 16

Prepared for: Slough Heat and Power Limited AECOM Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Non - Technical Summary

This document supports the application submitted by Slough Heat and Power Limited (“SHP”) under the Environmental Permitting (England and Wales) Regulations 2016 (“the EP Regulations”) (as amended) to vary the Environmental Permit for the Slough Heat and Power Station (“SHPS” or “the installation”) (permit reference: EPR/CP3031SX). This variation is being submitted to amend the maximum fuel throughput of the Multifuel facility at the SHPS to 480,000tpa. The installa- tion is located on 342 Edinburgh Avenue, Slough Trading Estate, Berkshire, SL1 4TU.

The installation’s Environmental Permit was varied in 2016 (application submitted in December 2014 (the “2014 Permit Variation”)) to add the operation of a Multifuel facility to the installation, comprising a new energy from waste (EfW) facility fired by refuse derived fuel (RDF) with a gross electrical out- put of 50MWe and a nominal thermal export of 10 – 20MWth as steam to the local heat network. The Multifuel facility will comprise two incineration lines (Boilers B18 and B19) and has been designed to operate using 480,000 tpa of fuel with Net Calorific Values (NCV) in the range of 10.5MJ/kg to 16MJ/kg, with the annual availability of 8,000 hours.

The Permit also includes an existing incineration activity for Boiler 17 (B17) which has a thermal in- put capacity of 69MW and a maximum fuel throughout of 120,000tpa. No changes are proposed to the operation of B17 as part of this variation.

The Multifuel facility has always been designed on the basis of combusting up to a maximum of 480,000tpa of fuel at the lower end of the fuel NCV range; however, the environmental impact assessment submitted to support the 2014 Permit Variation was undertaken on the basis of the nominal fuel NCV of around 12MJ/kg. Due to the considerable difference between the mass of fuel throughput at 12MJ/kg and 10.5MJ/kg (being 438,000tpa and 480,000tpa respectively), the Environment Agency (EA) was not satisfied that the air impact assessment was representative of the worst-case emissions scenario. The EA therefore issued the Permit based on a fuel throughput for the Multifuel facility of 438,000tpa in 2016. The Multifuel facility is not currently operational but is currently under construction.

This variation application is therefore being submitted, together with a revised air impact assessment to take account of the higher fuel throughput at the minimum fuel NCV of 10.5MJ/kg, in order to increase the permitted throughput of the Multifuel facility (B18 & B19) to 480,000tpa. This increases the total aggregated installation capacity for total waste fuel throughput (including B17) to 600,000tpa.

It is considered that the only pertinent change in the permitted Multifuel facility, is a change in the emissions to air and their associated environmental impact, due to the lower NCV fuel and the increased fuel throughput.

An assessment of the impact of emissions to air has been undertaken (Appendix B). This assessment has been updated from the 2014 assessment to reflect the maximum fuel throughput of the Multifuel facility, and also to incorporate updates on the data available in relation to the predicted emissions associated with the specific combustion technology, which has now been selected and is proposed to be installed (twin line plant from HZI). The ambient background and receptor data have also been updated to reflect current data available. The revised air quality impacts assessment con- cludes that the predicted level of impact is broadly the same for both the design fuel and minimum NCV fuel and materially lower than that predicted in the 2014 Permit Variation, due to an increase in the discharge temperature and efflux velocity, leading to improved dispersion of the emission.

The combustion gases will be treated in a flue gas treatment (FGT) plant prior to being discharged via a single stack (with two flues) (‘South Stack’). The stack will be 90m tall to allow appropriate dispersion of the treated flue gas.

The main emissions from the Multifuel facility will consist of combustion gases emitted to air. Due to the nature of the fuel used, such emissions will include nitrogen oxides (NOx), sulphur dioxide (SO2), other acid gases (hydrogen chloride (HCl) and hydrogen fluoride (HF)), dioxins and heavy metals (including mercury), and particulate matter. The FGT system will control and minimise the emissions of these pollutants, and will include a Selective Non-Catalytic Reduction (SNCR) system consisting of ammonia solution (or urea) injection for control of NOx; the injection of activated carbon to control

Prepared for: Slough Heat and Power Limited AECOM 1 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005 dioxins, mercury and heavy metal emissions; the injection of hydrated lime with wet conditioning (semi- dry scrubbing) to control acid gas emissions; and a fabric filter system to remove particulate matter.

Monitoring of point source emissions to air will be undertaken by certified continuous emissions monitoring systems (CEMS). In accordance with the waste incineration articles of the Industrial Emissions Directive (2010/75/EU), periodic measurements will be carried out four times in the first year of operation and twice per year thereafter.

Dust will be controlled through the enclosure of all potentially dusty operations within enclosed buildings, enclosed conveyor systems and sealed silos for controlling emissions of fly ash (Air Pollution Control residue (APCr)). Primary air for the boiler will be extracted from the tipping hall and fuel bunker, resulting in these areas being kept under a slight negative pressure, thereby minimising the potential for the escape of dust and also odours.

As the Multifuel facility has always been designed for a maximum throughput of 480,000tpa, no changes to site infrastructure are proposed by this variation application. There will be no changes to emissions to controlled waters or land due to the changes proposed by this variation application. There will be no process discharges to ground and groundwater from the Multifuel facility.

As described in the 2014 Permit Variation, emissions from the installation will include process effluents mainly consisting of boiler blowdown, which will be recirculated within the facility as far as reasonably practicable, typically through the ash quench system. Small quantities of process effluent will be discharged to sewer via emission points S1 – S4, however there will be no increase in the volume of process effluent or the quality of the effluent as a result of this variation application. The discharge to foul sewer will continue to be in compliance with the Trade Effluent Discharge Consent (ref: TSLO0433).

Uncontaminated surface water runoff from building roofs, hard-standings and hard landscaped areas will continue to be discharged to soakaways on-site or the existing culvert running along the northern edge of Edinburgh Avenue, via emission points W1 and W2. There will therefore not be any change in the impact on the emissions to water from the Multifuel facility.

The quantity of waste arising from the Multifuel facility in the 2014 Permit Variation was estimated based on the nominal fuel NCV of 12MJ/kg. Therefore, it is estimated that for the lower fuel NCV of 10.5MJ/kg the quantity of bottom ash and APCr produced will increase to approximately 96,000tpa and 20,000tpa respectively. The storage, handling and management of these wastes will be in line with the procedures proposed in the 2014 Permit Variation.

As there are no major changes to any of the plant or equipment proposed for the Multifuel facility, and as an existing permitted operation, the Multifuel facility will comply with the requirements of the Waste Incineration BAT Reference document (WI-BRef) 2006. The requirements of the revised 2019 BRef will be required to be met by December 2023. The BAT assessment undertaken for the Multifuel facility in the 2014 Permit Variation is therefore still applicable, and no additional BAT assessment has been undertaken for this variation application.

The Multifuel facility will continue to operate as per the ISO14001 accredited Environmental Management System (EMS) already in place for the installation.

The energy efficiency of the Multifuel facility has been estimated based on the BAT associated energy efficiency levels (BAT-AEELs) established in the WI BRef 2006. Based on the revised fuel throughput of 480,000tpa, the Multifuel facility will generate approximately 10.4MWe per 100,000 annual tonnes of waste throughput. The efficiency of the Multifuel facility therefore exceeds the benchmark efficiency range of 5MWe to 9MWe per 100,000tpa of throughput. Additionally, based on a total electrical output of 400,000MWh/year, the Multifuel facility will generate approximately 0.83MWh/tonne of waste, exceeding the upper range of the benchmark range of 0.415 - 0.644 MWh/tonne of waste for electricity production per tonne of municipal solid waste (MSW).

The specific energy consumption for the Multifuel facility, estimated based on the parasitic load of 5MWe, will remain approximately 100kWh/t as outlined in the 2014 Permit Variation. This is comparable to the WI BRef 2006 benchmark of 150kWh/t. The Multifuel facility will therefore continue to achieve the benchmark levels for energy efficiency from both the BAT Incineration Sector Guidance Note and the BREF for waste incineration.

Prepared for: Slough Heat and Power Limited AECOM 2 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

The Multifuel facility will generate up to 50MW of electricity through the combustion of RDF, of which approximately 45MW will be available for export to the distribution networks, and between 10 and 20MW of steam for export to the local heat network for the Slough Trading Estate. Additional steam may be available to export to the local heat network whilst maintaining an electrical output of 50MW. All technical aspects of the Multifuel facility, including but not limited to the combustion system, will remain as per the details provided in the 2014 Permit Variation.

This application does not propose any change to the installation boundary or the design storage capacity of RDF and other raw materials. Additional assessment of baseline conditions is therefore not considered to be required.

The procedures for site closure at the end of design life will remain the same.

The higher fuel throughput of the Multifuel facility does not, therefore, result in any adverse environmental impact.

Prepared for: Slough Heat and Power Limited AECOM 3 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Introduction

This document supports an Environmental Permit variation application submitted by Slough Heat and Power Limited (“SHP”) under the Environmental Permitting (England and Wales) Regulations 2016 (“the EP Regulations”) (as amended) to vary the Environmental Permit for the Slough Heat and Power Station (“SHPS” or “the installation”) (permit reference: EPR/CP3031SX/V003) located on 342 Edinburgh Avenue, Slough Trading Estate, Berkshire, SL1 4TU.

The latest version of the Environmental Permit for the installation was issued by the Environment Agency (EA) in 2016 to include the operation of a new proposed Multifuel facility at the installation. The Multifuel facility is not currently operational but is currently under construction. The location of the installation is shown in Figure 1 whilst the layout and boundary of the Multifuel facility are shown in Figure 2 (figures are provided in Appendix A). The Environmental Permit currently allows a maximum Refuse Derived Fuel (RDF) throughput of 438,000 tonnes per annum (tpa) for the Multifuel facility, based on the environmental impact assessment undertaken in support of the Environmental Permit Variation application submitted in December 2014 (“2014 Permit Variation”). The 2014 Permit Variation stated that the Multifuel facility will be designed to be combust RDF having a nominal fuel net calorific value (NCV) of approximately 12MJ/kg, with the design NCV range of circa 10.5 – 16MJ/kg. Although most aspects of the 2014 Permit Variation were prepared based on the maximum annual fuel throughput of 480,000tpa, the air quality impact assessment undertaken to support the application was based upon the nominal design NCV of the fuel (12MJ/kg) rather than the lower end of the stated NCV range (10.5MJ/kg), and therefore did not consider the maximum possible fuel throughput. Consequently, the EA was not satisfied that the operator had appropriately considered the potential worst-case environmental impact of the Multifuel facility. Subsequently, the Environmental Permit issued to SHP was based on the lower RDF volume of 438,000tpa, associated with the nominal fuel NCV of 12MJ/kg. A variation to the current Environmental Permit is now being sought for an increase in the permitted RDF throughput for the Multifuel facility to 480,000tpa, and an updated air impact assessment, based on the emissions associated with the lower end of the stated NCV range (10.5MJ/kg), has been submitted to support this variation application.

2.1 Background The SHPS installation is mainly located on the south side of Edinburgh Avenue, within the Slough Trading Estate. The installation was previously permitted for electricity and steam generation as a co- incineration plant via combustion of coal, wood waste, biomass, natural gas and waste fractions (comprising fibrefuel pellets manufactured on site from municipal solid waste (MSW)). These activities in two circulating fluidised bed boilers along with 2 gas-fired boilers and a gas turbine/ waste heat boiler were removed from the Environmental Permit as part of the 2014 Permit Variation.

The 2014 Permit Variation requested the addition of a new steam turbine, (referred to as ‘Turbine 18’) having an electrical output of 50MW, to the installation’s Environmental Permit, allowing the com- bustion of RDF only to generate electricity. The varied site operations included repurposing some of the existing site infrastructure to utilise it for the revised operations including, but not limited to, the cool- ing towers located on site.

SHPS provides various services to the Slough Trading Estate, including electricity distribution and the distribution and supply of heat and potable water, as well as other ancillary services such as water treatment, operations and maintenance and cooling water. These activities continue to be covered under the Permit.

The 2014 Permit Variation proposed a number of changes to existing site infrastructure and addition of new plant to allow the site to operate as a Multifuel facility, designed to combust up to a maximum of 480,000tpa of RDF.

The Multifuel facility has the designed nominal availability of 8,000 hours per year; accepting fuel having NCV range of 10.5 – 16MJ/kg. The designed maximum combined thermal input to the facility is

Prepared for: Slough Heat and Power Limited AECOM 4 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

approximately 183MWth, based on a maximum fuel throughput of 480,000tpa with a minimum fuel NCV of 10.5MJ/kg. The thermal input capacity of the final plant design has also been increased by around 10% compared to the 2014 Permit Variation to accommodate a more conservative boiler design (lower temperature and pressure) aimed at achieving high plant availability in order to:

· Maximise the supply of low carbon heat to the SHP network; · Minimise waste derived fuel interruptions; and, · Minimise periods with no boiler air extraction for odour control. The nominal design NCV of fuel for the Multifuel facility is 12.06MJ/kg and the impact assessment of anticipated emissions to air were based on this value for the 2014 Permit Variation. The EA stated that despite the conservative approach to determining the air quality impacts at that time, the significant difference in tonnage between the design fuel assessed (438,000tpa) and the maximum potential input (480,000tpa) when using an RDF with a lower NCV was “considered to be too great not to appropriately assess”. The revised Environmental Permit was therefore based on the impact assessment undertaken for the Multifuel facility (and the associated nominal fuel throughput) and not the maximum design input.

The permit also includes a separate incineration activity for Boiler 17 (B17) which has a thermal input capacity of 69MW and a maximum fuel throughout of 120,000tpa. No changes are proposed to the operation of B17 as part of this variation.

2.2 Proposed Variation It is proposed to vary the Environmental Permit to reflect the full design range of the Multifuel facility which has the designed nominal availability of 8,000 hours per year; accepting fuel having NCV range of 10.5 – 16MJ/kg. The designed maximum combined thermal input to the Multifuel facility is approximately 183MWth, based on a maximum fuel throughput of 480,000tpa at the minimum fuel NCV of 10.5MJ/kg. Where fuel with an NCV of greater than 10.5MJ/kg is used, the mass throughput of waste would be proportionately lower.

An assessment of impacts of emissions to air from combustion of up to 480,000tpa of RDF with an NCV of 10.5MJ/kg has therefore been carried out as part of this variation application and is included in Appendix B of this document.

It should be noted that, although the air quality impact assessment has been undertaken for the increased RDF throughput to the Multifuel facility for the purpose of this variation application, no other changes are proposed. The design of the Multifuel facility in the 2014 Permit Variation was based on a maximum annual RDF throughput of 480,000tpa, and therefore included appropriate infrastructure and utility connections to handle, store and treat the 480,000tpa throughput at this time. Therefore, in order to avoid repetition, the Multifuel facility design description has not been updated in this application document.

It is therefore proposed to vary Table S2.2 of the existing Permit to allow a maximum aggregated annual throughput to the installation of 600,000tpa from the current 558,000tpa, with the input capacity of the Multifuel facility to be increased from 438,000tpa to 480,000tpa (in Boilers 18 and 19) and the input to Boiler 17 remaining unchanged at 120,000tpa.

In addition to this, the wording of the introductory note on page 3 of the Permit should be amended to reflect the maximum capacities detailed above.

No other changes are proposed to Schedules 1 – 5 of the existing Permit.

Schedule 5 Part 1 Paragraph 5 (5) of the EP Regulations defines a substantial change to an Environmental Permit as below:

“substantial change” means a change in operation of an installation which in the regulator’s opinion may have significant negative effects on human beings or the environment and includes—

(a) in relation to a Part A installation, a change in operation which in itself meets the thresholds, if any, set out in Part 2 of Schedule 1, and

Prepared for: Slough Heat and Power Limited AECOM 5 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

(b) in relation to a waste incineration plant or waste co-incineration plant for non-hazardous waste, a change in operation which would involve the incineration or co-incineration of hazardous waste.

As the proposed increase in the fuel throughput to the Multifuel facility is greater than 3t/hour, it is considered to meet the throughput threshold of EP Regulations Schedule 1 Part 2 Chapter 5.1 Part A(1)(b) (the incineration of non-hazardous waste in a waste incineration plant or waste co-incineration plant with a capacity exceeding 3 tonnes per hour), and therefore represents a “substantial change” to the permitted operations. Consequently, this application is being submitted as a Substantial Permit Variation application.

In addition to the change in fuel throughput, a minor change to the Water Treatment Plant (WTP) that was proposed in the 2014 Permit Variation has also occurred. At the time of the 2014 Permit Variation, it was proposed that a new Reverse Osmosis (RO) and Electro-deionisation (EDI) plant be installed at the installation, to replace an existing RO-demin plant combination. The EDI plant would not have required any bulk chemical storage for water treatment activities.

However, the plant that has now been installed is an RO and mixed bed deioniser WTP. This is located in the old Fibre Fuel Building. As the WTP is a mixed bed deioniser plant, there is a need for regeneration chemicals to be stored in new bulk tanks. The bulk tanks are polyprop and have their own integral bunding that is 110% of the tanks’ size. This WTP replaces an old Reverse Osmosis plant and demin combination, and therefore the type of chemicals to be stored on site are as per the original permit, however the quantities required for the new WTP are much lower than those originally stored at the installation.

In addition to this WTP, an additional RO plant with an EDI and a final mixed bed filter is required specifically for the Multifuel facility. It will be located under the tipping floor of the Multifuel facility and will be independent from the WTP detailed above. It is anticipated that the Multifuel RO plant will be up to five streams, with the effluent either draining to the Multifuel wastewater collection system or to be used as boiler spray water. Any regeneration chemicals will be stored in appropriate tanks with bunding capable of holding 110% of the tanks’ volume, and again will be required in quantities that will be much lower than those originally stored at the installation.

2.3 Environmental Setting The SHPS installation is located on the Slough Trading Estate, which lies within the Thames Valley approximately 4km north of the River Thames and is surrounded by the conurbation of Slough. Windsor is approximately 5km south and Maidenhead is approximately 7km west of the SHPS installation. The approximate National Grid Reference of the centre of the installation is SU953814.

The installation is located mainly on the south side of Edinburgh Avenue, with two associated natural draught cooling towers occupying an area immediately to the north of Edinburgh Avenue.

The surrounding area is characterised by a mix of industrial and commercial use in the trading estate, with residential areas located around the trading estate. Immediately beyond the residential areas are agricultural fields and parks. Other towns including Burnham, Farnham Royal, Stoke Green, Taplow, Wexham, Windsor and Maidenhead are located within 5km of the Site.

There have been no changes to the site setting since the Permit was issued, and no changes to installation boundary are proposed by this variation application.

Site Condition

This application to vary the Environmental Permit does not propose any amendment to the existing installation boundary or the addition of any infrastructure. The risks to ground, groundwater and surface water from the Multifuel facility therefore remain the same as covered in the 2014 Permit Variation. The Site Condition Report submitted as part of the 2014 Permit Variation is considered to continue to apply to the installation. Therefore, additional risk assessment or amendment to the current Site Condition Report has not been undertaken.

Prepared for: Slough Heat and Power Limited AECOM 6 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Operating Techniques

4.1 Technical Standards The Multifuel facility will operate in accordance with the applicable EA Sector Guidance, namely:

· How to comply with your environmental permit additional guidance for: The Incineration of Waste (EPR 5.01)1; · Best Available Techniques (BAT) Reference Document for Waste Incineration2 (WI BRef); and · Environmental Permitting Guidance: Waste Incineration3. The WI BRef was revised in December 2019, however, as the Multifuel facility has an existing Permit it does not need to demonstrate compliance with the revised BRef until December 2023 (4 years from its publication). Therefore, based on the pre-application advice provided by the EA, it is considered that the demonstration of compliance with the previous version of the WI BRef (published in 2006) continues to be relevant for the Multifuel facility, and no assessment of BAT compliance is required with respect to the revised BRef as part of this variation application.

In addition, the Multifuel facility will operate in accordance with appropriate management systems developed in line with EA guidance, as described in Section 2.8 of the 2014 Permit Variation application Supporting Document4 and as submitted by SHP to the EA for completing the requirements of Improvement Condition (IC) 10 of the Permit.

As a result of this variation, the Multifuel facility will have the capability to combust up to 60 tonnes per hour of RDF, based on annual throughput of up to 480,000tpa and 8,000 annual operating hours. The proposed activity therefore continues to be covered under Section 5.1 Part A(1) (b) of the EP Regulations as an activity for ‘the incineration of non-hazardous waste in a waste incineration plant or waste co-incineration plant with a capacity exceeding 3 tonnes per hour’.

4.2 Process Description The Multifuel facility’s operations will continue to be in line with the description provided in the 2014 Permit Variation. In order to avoid repetition, these descriptions have not been provided in this variation application, although reference to the relevant sections of the 2014 Permit Variation have been made, as appropriate.

A description of the operating techniques to be implemented at the Multifuel facility is provided in Section 1.5 of the Supporting Document submitted with the 2014 Permit Variation.

Since the collation of the documentation for the 2014 Permit variation, the project has continued to develop, and a specific combustion technology for the Multifuel facility has now been selected and is proposed to be installed. This is proposed to be a twin line plant supplied by HZI. Whilst this specific technology does not materially change the nature of the Permit or the conditions therein, it has allowed more accurate process and emissions data to be collated for inclusion in this document and the air quality impact assessment (Appendix B).

The Multifuel facility will receive up to 480,000tpa of pre-processed RDF having NCV in the range of 10.5 MJ/kg to 16 MJ/kg for combustion in two combustion lines, or a combined thermal input of 183MWth. The Multifuel facility will generate up to 50MW of gross electrical output, whilst also exporting up to 20MWth of heat to supply the existing Slough Trading Estate heat network. Recovered heat can be supplied to the heat customers in the form of steam via extraction of steam from the steam turbine at low pressure.

The Multifuel facility will only accept waste streams permitted to be accepted (as listed in Schedule 2 of the Permit). Only pre-processed RDF (having had the recyclable fraction removed) able to meet a

1 How to comply with your environmental permit Additional guidance for: The Incineration of Waste (EPR 5.01), EA, March 2009 2 Best Available Techniques (BAT) Reference Document for Waste Incineration, European IPPC Bureau, 2006 3 Environmental Permitting Guidance: Waste Incineration, Department for Environment Food & Rural Affairs, updated 22nd December 2015 4 Slough Heat and Power Slough Multifuel Supporting Information, Fichtner Consulting Engineers Ltd for Slough Heat and Power Ltd, December 2014

Prepared for: Slough Heat and Power Limited AECOM 7 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005 pre-determined fuel composition range (as described in the 2014 Permit Variation) will be sourced and accepted at the Multifuel facility. The Multifuel facility will not accept or combust any hazardous waste.

The Multifuel facility will continue to implement the pre-acceptance, acceptance, rejection, quarantine and other relevant procedures and protocols put in place as part of 2014 Permit Variation. All waste procedures were developed on the basis of the maximum fuel throughput of 480,000tpa. Details of the RDF reception area and Tipping Hall are as per Section 1.5.2 of the Supporting Document of the 2014 Permit Variation.

The combustion system will comprise a two-stream combustion unit. A moving grate design will ensure continuous mixing of the fuel and hence promote good combustion. Details of the combustion system, including the use of primary air, is provided in Section 1.5.4 of the Supporting Document of the 2014 Permit Variation and remain unchanged by this variation application.

The Multifuel facility will include flue gas treatment (FGT) systems for removal of pollutants from the flue gas prior to discharge to atmosphere; details of the FGT systems implemented at the Multifuel facility are provided in Section 1.5.6 of the Supporting Document of the 2014 Permit Variation. The flue gases will be treated using hydrated lime with wet conditioning to neutralise the acid gases. Activ- ated carbon will be injected into the flue gases preceding the bag filter to adsorb (primarily) dioxins, other volatile organic compounds (VOCs), mercury and other trace metals. The hydrated lime injection rate will be controlled by upstream measurement of hydrogen chloride (HCl) thus optimising the effi- ciency of gas scrubbing and hydrated lime usage. Nitrogen oxides (NOx) abatement will be achieved by the use of Selective Non-Catalytic Reduction (SNCR). The SNCR is based on the in- jection of ammonia solution (or urea) into the furnace chambers. Bag filters will be used to remove the fine ash plus excess spent hydrated lime and carbon as the flue gases pass through the bag filter fabric.

The Multifuel facility will include dedicated duty Continuous Emissions Monitoring Systems (CEMS) for each line and a further hot stand-by CEMS, which will ensure that there is continuous monitoring data available even if there is a problem with a duty CEMS. Substances that will be monitored continuously will include oxygen, carbon monoxide, hydrogen chloride, sulphur dioxide, nitrogen oxides, ammonia, VOCs, and particulates. Other pollutants will be monitored by spot measurements at regular intervals. The monitoring data will be recorded, and operators will be alerted if emissions to air approach authorised limits. The results of the monitoring will be reported to the EA. Details of the proposed monitoring regime for emissions to air from the Multifuel facility are provided in Section 1.5.9 of the Supporting Document of the 2014 Permit Variation and in Tables S3.1 and S3.1a of the permit.

Descriptions of ancillary operations comprising the demineralised water supply, firefighting system, emergency back-up system (or a standby generation system) and the cooling systems is provided in Section 1.5.7 and 1.6 of the Supporting Document of the 2014 Permit Variation and remain un- changed.

In addition to the change in fuel throughput, a minor change to the Water Treatment Plant that was proposed in the 2014 Permit Variation, is also planned. At the time of the 2014 Permit Variation, it was proposed that a new Reverse Osmosis (RO) and Electro-deionisation (EDI) plant be installed, to replace an existing RO plant. The EDI plant would not have required any bulk chemical storage for water treatment activities.

However, the plant that has now been installed is an RO and mixed bed deioniser WTP. This is located in the old Fibre Fuel Building. As the WTP is a mixed bed deioniser plant, there is a need for regeneration chemicals (sodium bisulphate (200 litre tank), anti-scalent (500 litre tank), sodium hydroxide and hydrochloric acid (both 3,000 litre tanks)) to be stored in new polypropylene bulk tanks. The bulk tanks have their own integral bunding that is 110% of the tanks’ size. This WTP replaces an old Reverse Osmosis plant and demin combination, and therefore the type of chemicals to be stored on site are as per the original permit. The quantities of these raw materials are much lower than those previously stored at the installation, for example the old hydrochloric acid tank was 60,000l. In addition, due to the smaller quantities of these chemicals to be stored, delivery of these raw materials will now be in the form of IBC’s rather than by tanker, as would previously have been required.

In addition to this WTP, an additional RO plant with an EDI and a final mixed bed filter is required specifically for the Multifuel facility. It will be located under the tipping floor of the Multifuel facility and will be independent from the WTP detailed above. It is anticipated that the Multifuel RO plant will be up to five streams with approx 8m3/hr capacity each. It is anticipated that each stream will operate at Prepared for: Slough Heat and Power Limited AECOM 8 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

30% of the capacity required, providing inbuilt redundancy. The effluent produced will either drain to the Multifuel wastewater collection system or be used as boiler spray water.

Any regeneration chemicals will be stored in appropriate tanks with bunding capable of holding 110% of the tanks’ volume. It is envisaged that the chemicals and quantities required will be less than those for the new WTP plant that has been installed in the old Fibre Fuel Building.

The locations of the WTP and RO plant are shown on Figure 2 (Appendix A).

The Multifuel facility will continue to be controlled from the dedicated control room via an automated control system to control operations, optimising the process relative to efficient heat release, good burn- out and minimum particle carry-over. Details of proposed process monitoring are provided in Section 2.3.2 of the Supporting Document of the 2014 Permit Variation.

4.3 Raw Materials The 2014 Permit Variation outlined that the Multifuel facility is designed on the basis of handling up to a maximum of 480,000tpa of fuel. Therefore, additional raw materials or storage facilities are not required for the changes proposed by this variation application.

The key raw material will be the RDF used as fuel at the Multifuel facility. The fuel storage bunker will be located to the east of the boiler house, and have a storage capacity of approximately 5,000 tonnes, which is equivalent to approximately 4 days fuel throughput. The maximum fuel storage capacity of the Multifuel facility i.e. 5,000 tonnes remains the same and has not changed as a result of this variation application.

The type and quantities of raw materials used at the Multifuel facility will be limited to those specified in Table 2.1 of the Supporting Document of the 2014 Permit Variation and Schedule 2 of the existing Permit.

In terms of the water treatment chemicals, the 2014 Permit Variation stated that <100 tonnes of water treatment chemicals would be used per annum. Indicative annual quantities of chemicals required for the WTP plant are 20 tonnes of sodium hydroxide and 25 tonnes of hydrochloric acid, and therefore remain under the 100 tonnes stated in the 2014 Permit Variation. It is anticipated that the new RO plant for the Mutlifuel facility will require lower quantities of chemicals than the WTP plant, therefore total usage will remain below the 100 tonnes per annum detailed in the 2014 Permit Variation.

4.4 Waste The type of the wastes produced by the Multifuel facility, including but not limited to bottom ash, Air Pollution Control residue (APCr), and their management, will remain as described in Section 2.7 of the Supporting Document of the 2014 Permit Variation.

In view of the maximum fuel throughput to the facility (at a lower NCV) being higher than that assessed in the 2014 Permit Variation it is estimated that the quantity of bottom ash and APCr will increase accordingly. The estimated maximum bottom ash and APCr quantities for the Multifuel facility based on the changes proposed by this application are shown below in Table 4-1.

Table 4-1: Key Residue Streams from the Multifuel Facility

Source/ Material Properties of Residue Storage Location Anticipated Annual Quantity (tpa) (a) Bottom Ash Grate ash, grate riddlings, boiler Bottom ash storage 96,000 (b) ash. This ash is relatively inert, bunker. No change in classified as non-hazardous. storage capacity of the bunker as bunker sized to maximum ash quantity. APCr (Fly ash) Fly ash and dry flue gas Two APCR silos. No 20,000 treatment residues, which may change in storage capacity contain some unreacted of the silos as silos sized to hydrated lime. maximum ash quantity. Notes:

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Source/ Material Properties of Residue Storage Location Anticipated Annual Quantity (tpa) (a) (a) The annual tonnage of ash has been estimated on the basis of 16.8% ash content and 20% water content. (b) The bottom ash estimate includes 4,015tpa of boiler ash.

SHP has completed an audit of waste management methods to be implemented at the installation in line with IC11 of the existing Permit. The audit included an assessment of best practical environmental options for the disposal of wastes, identification of dedicated waste storage areas, their capacities and maximum retention times on site, and an assessment of the materials intended for combustion at the site. As the waste quantities are envisaged to only rise marginally compared to the 2014 Permit Vari- ation, the waste minimisation audit is considered to continue to apply to the Multifuel facility and ad- ditional assessment is not required.

4.5 Energy Use Based on a heat balance calculation for a fuel throughput at an NCV of 10.5MJ/kg, it is estimated that the Multifuel facility will require approximately 5MWe for plant operation. The thermal input or output of the Multifuel facility will remain unchanged by this variation application, since the proposed higher throughput of 480,000tpa will be the lower end of the fuel NCV range (10.5MJ/kg) instead of the nominal NCV of 12.06MJ/kg.

4.5.1 Energy Efficiency As an existing installation, the energy efficiency of the Multifuel facility has been estimated on the basis of the benchmarks set in the WI BRef published in 2006. The energy efficiency estimate for the nominal waste throughput is shown in Section 2.6.3 of the Supporting Document of the 2014 Permit Variation.

According to the WI BRef 2006, between 5MWe to 9MWe of energy should be recoverable per 100,000 annual tonnes of waste. The plant will generate up to 50MWe from a maximum design capacity of 480,000tpa. This equates to approximately 10.4MW per 100,000 annual tonnes of waste throughput, assuming the maximum design capacity. The efficiency of the proposed plant therefore exceeds the benchmark efficiency figures, demonstrating the high efficiency of the plant.

On the basis of the Multifuel facility being available for 8,000 hours per annum, allowing for periods of start-up or shutdown, it will generate 400,000MWh per annum. Therefore, the Multifuel facility will generate approximately 0.83MWh/tonne of waste, at the maximum design throughput of 480,000tpa. This significantly exceeds the upper range of the benchmark range of 0.415 - 0.644 MWh/tonne of waste for electricity production per tonne of MSW (there are no benchmarks for the incineration of ‘pre- processed’ waste), as presented in the WI BRef 2006.

The specific energy consumption for the Multifuel facility, estimated based on the parasitic load of the facility (5MWe) will remain approximately 100kWh/t, which is the same as was detailed in the 2014 Permit Variation.

The Multifuel facility will therefore continue to achieve the benchmark levels for energy efficiency from both the BAT Incineration Sector Guidance Note and the WI BRef.

The generated steam will supply a steam turbine to generate electricity. The Multifuel facility will supply electricity via a power transformer which will increase the voltage to the appropriate level.

The plant has been designed with careful attention being paid to all normal energy efficiency design features, such as high efficiency motors, high standards of cladding and insulation etc. The plant has been designed to achieve a high thermal efficiency with high steam parameters and good burnout quality.

4.5.2 Further Energy Efficiency Requirements The Multifuel facility is not subject to a Climate Change Levy agreement and is exempt from the European Union Emissions Trading Scheme (EUETS).

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The Multifuel facility will continue to operate in accordance with the Heat Plan provided in Annex 7 of the Supporting Document of the 2014 Permit Variation. The Multifuel facility will export up to 20MWth heat to the Slough Trading Estate, and therefore has been designed to be CHP-Ready.

The amount of heat exported will fluctuate dependant on the heat demand of users within the Trading Estate. As the Multifuel facility has been designed and will operate as a CHP plant, it is considered to represent BAT for energy efficiency, and a CHP Readiness (CHP-R) assessment is not required.

4.6 Operating and Maintenance Procedures The operating and maintenance (O&M) procedures for the installation will remain as outlined in Section 2.6.4 of the 2014 Permit Variation.

4.7 Management Systems The existing ISO 14001 accredited environmental management system (EMS) for the installation (as completed for IC10) will be implemented to the Multifuel facility.

4.8 General Maintenance All equipment within the Multifuel facility will be subject to a Planned and Preventative Maintenance Programme, where appropriate, to minimise unplanned failures. The existing maintenance procedures and programmes for the Multifuel facility were prepared to handle 480,000tpa of fuel and will therefore not require to be updated to reflect this variation application.

Emissions to Air, Water and Land

5.1 Emissions to Air

5.1.1 Source Characterisation There is one main point source release to air from the Multifuel facility (Release Point identified as ‘South Stack flue 1, 2’), with another emission point from the existing Boiler 17 (Release Points identified as ‘North Stack flue 1, 2, 3’) and Package Boiler. In addition to these releases there are a number of pressure relief valves for the storage tanks at the installation which are part of the plant emergency protection arrangements. All release sources are identified in Table 5-1 below.

Table 5-1: Point Source Releases to Air from the Installation Point Reference Plant Source Emissions

South Stack 1, 2 Multifuel lines 1 & 2 Oxides of nitrogen (NOx) (Boilers 18 & 19) - Sulphur dioxide (SO2) Combustion of RDF Carbon monoxide (CO) Particulate matter (PM) Volatile organic carbons (VOCs) Hydrogen chloride (HCl) Hydrogen fluoride (HF) Metals (Arsenic (As), Cadmium (Cd), Chromium (Cr), Cobalt (Co), Copper (Cu), Lead (Pb), Manganese (Mn), Nickel (Ni), Selenium (Se), Vanadium (V) and Zinc (Zn)) Dioxins and furans (PCDDs, PCDFs)

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Point Reference Plant Source Emissions North Stack 1,2,3 Boiler 17 – Oxides of nitrogen (NOx) Combustion of wood Sulphur dioxide (SO2) waste or waste Carbon monoxide (CO) derived fuel Particulate matter (PM) Volatile organic carbons (VOCs) Hydrogen chloride (HCl) Hydrogen fluoride (HF) Metals (Arsenic (As), Cadmium (Cd), Chromium (Cr), Cobalt (Co), Copper (Cu), Lead (Pb), Manganese (Mn), Nickel (Ni), Selenium (Se), Vanadium (V) and Zinc (Zn)) Dioxins and furans (PCDDs, PCDFs) Package Boiler Package Boiler firing Oxides of nitrogen (NOx) natural gas Carbon monoxide (CO)

5.1.2 Stack Characteristics The principal source of emissions to atmosphere from the normal operation of the Multifuel facility will be from the 90 metre South Stack, which comprises two flues, one from each of the two combustion lines. Emissions will include oxides of nitrogen, sulphur dioxide, particulate matter, trace metals, organic compounds and carbon monoxide. The dimensions of the South Stack are shown in Table 5-2.

Table 5-2: South Stack at Operational Design Load (10.5MJ/kg) Parameter Unit South Stack 1, 2 (Multifuel lines 1 and 2) Stack position (NGR) m 495262, 181460 Stack release height (above ground level) m 90 Effective internal stack diameter m 2.68 Flue temperature °C 150 Moisture content % Volume 20.5

Flue O2 content (dry) % 6.1 Efflux velocity Am/s 24.3 Stack flow (actual) Am3/s 137.0 Stack flow at reference conditions (STP, dry)(a) Nm3/s 105.1 Note: (a) Normalised to 0ºC, 101kPa, Dry at 11% oxygen (b) Normalisation takes account of emission temperature, pressure, moisture and oxygen content

5.1.3 Emissions Inventory Proposed emission limit value (ELV) benchmarks for the Multifuel facility are as defined in the WI BRef (2006) and the IED, as shown in Table 5-3.

Table 5-3: Emission Limit Values for the South Stack

Parameter Daily Average Emissions Half-Hour Average (IED ELVs) (BAT-AEL) mg/Nm3 mg/Nm3

NOx (as NO2) 200 400

Total Particulates (assumed as PM10) 10 30

SO2 50 200

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Parameter Daily Average Emissions Half-Hour Average (IED ELVs) (BAT-AEL) mg/Nm3 mg/Nm3 TOC (as Benzene) 10 20 CO 50 100 HCl 10 60 HF 1 4 Group 1 metals (Cd + Tl, total) 0.05 - Group 2 metals (Hg) 0.05 - Group 3 metals (Sb + As + Pb + Cr + Co 0.5 - + Cu + Mn + Ni + V, total) Dioxins and furans 0.1ng/m3 - Ammonia 5 -

The Air Quality assessment for the Multifuel facility is provided in Appendix B. This assessment has been updated from the 2014 assessment to reflect the maximum fuel throughput of the Multifuel Facility (480,000 tpa at a fuel NCV of 10.5MJ/kg) and also to incorporate updates on the data available in relation to the predicted emissions associated with the specific combustion technology which has now been selected and is proposed to be installed (twin line plant from HZI). The ambient background and receptor data have also been updated to reflect current data available.

The air quality assessment report presents a summary of the predicted impacts for the proposed plant combustion technology (at maximum fuel throughput at the lowest fuel NCV) compared to those reported in the 2014 Permit Variation shown in Table 4.1 of that report. It is considered that the modelling results associated with the lower NCV fuel are comparable with those reported for the 2014 Permit Variation, with impacts at human health receptors predicted to be below those reported in the dispersion modelling assessment carried out at that time.

The location of the release point for emissions to air for the Multifuel facility is shown in Figure 2 (Appendix A).

5.1.4 Fugitive Emissions to Air Dust The Multifuel facility design has always been based on the higher waste volume proposed by this variation application; therefore, there will not be any increased risk of dust emissions as a result of this variation application. Dust minimisation and management measures provided in Section 1.5.2 of the Supporting Document of the 2014 Permit Variation will continue to apply to the Multifuel facility.

Litter Litter prevention controls including the covering of vehicles delivering the RDF, along with tipping and storage of RDF within the enclosed tipping hall, as outlined in Section 1.5.2 of the Supporting Document of the 2014 Permit Variation, will continue to apply to the Multifuel facility.

5.2 Emissions to Water This variation is not anticipated to lead to any change in the emissions to water from the installation.

Process wastewater from the Multifuel facility, mainly consisting of boiler blowdown, will be recirculated where possible, typically through the ash quench system. No contaminated wastewater will be discharged to controlled waters.

As stated in Section 2.2.4 of the Supporting Document of the 2014 Permit Variation, the Multifuel facility will give rise to surface water run-off from roads, vehicle parking areas, building roofs, hard-standings and hard landscaped areas. Collected surface water from the stores yard and roofing run-off will continue to be discharged to soakaways on-site or the existing culvert running along the northern edge of Edinburgh Avenue, referred to as W1 within the existing Permit. Collected surface water from the

Prepared for: Slough Heat and Power Limited AECOM 13 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005 fibre fuel yard will be discharged to the existing emission point via an interceptor, referred to as W2 within the existing Permit. The location of the emission points W1 and W2 are shown in Figure 2.

As the facility is designed on the basis of the maximum fuel throughput of 480,000tpa, it is considered that no additional firewater storage or management will be required to address the changes proposed by this variation.

Firewater containment will be in accordance with the requirements of the Pollution Prevention Guidelines (PPG) 185 and the Combustion Technical Guidance Note6, with containment measures identified by SHP detailed in their response to IC5 of the Permit.

5.3 Emissions to Sewer As per Section 1.5.8 of the Supporting Document of the 2014 Permit Variation, any effluent that cannot be recirculated within site operations (expected to typically be within the ash quench system) would be discharged to the foul sewer via emission points S1 – S4 (see Figure 2 for location) in accordance with the existing Trade Effluent Discharge Consent (Ref: TSLO0433, dated 19th August 2008).

There will be no change in the volume, composition or method of handling for discharges to the sewer due to the increased fuel throughput.

The Water Treatment Plant drains to S2, which received effluent from the previous RO and demin plants on site and as detailed in the 2014 Variation. There will therefore be no change to this emis- sion.

5.4 Emissions to Land There will be no direct discharge to land from the Multifuel facility. All operations will be situated on concrete hardstanding with sealed drainage, so as to prevent accidental loss of materials to ground, and consequently affecting groundwater.

5.5 Odour The potential for odour releases from the Multifuel facility will not increase from the 2014 Permit Variation as a result of the increased fuel throughput, as the Multifuel facility design was originally based on the maximum RDF volumes proposed by this variation application (480,000tpa). The Odour BAT Assessment7 undertaken in support of the 2014 Permit Variation and the odour mitigation measures provided in Section 2.2.3 of the Supporting Document for the 2014 Permit Variation will continue to apply to the Multifuel facility.

As per pre-operational (PO) condition 1 of the existing Permit, the operator will prepare an Odour Management Plan and submit to the EA prior to commissioning of the Multifuel facility.

5.6 Noise The Multifuel facility has been designed to ensure that there are no impulsive or tonal features from its operation. The Multifuel facility was originally designed on the basis of plant and infrastructure handling an annual throughput of 480,000tpa. Therefore, the noise emission assessment undertaken as part of the 2014 Permit Variation (Annex 3 of the Supporting Document) is therefore still considered to be applicable to the Multifuel facility, and additional noise assessment is not considered to be required for this variation application.

The original assessment of noise impacts concluded that there were no significant effects on the noise sensitive receptors (NSRs) in the vicinity of the installation.

5.7 Heat The increased fuel throughput volume proposed by this variation application would not result in an increase in electrical or thermal output from the Multifuel facility. As stated in Section 1.5.1 of the Supporting Document for the 2014 Permit Variation, the Multifuel facility will generate electricity via 5 Managing Fire Water and Major Spillages: PPG18, EA and SEPA, June 2000, withdrawn in 2015 6 How to comply with your environmental permit Additional guidance for: Combustion Activities (EPR 1.01), EA, March 2009, withdrawn on 24th August 2018 7 Multifuel Energy Limited, Slough Multifuel, Odour Bat Assessment, ref: S1515-0500-0001JRS, Fichtner Ltd, September 2013

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Monitoring

6.1 Infrastructure No new infrastructure will be installed due to the changes proposed by this variation application. The installation’s infrastructure will continue to be monitored as per the site EMS.

6.2 Emissions to Air Monitoring of emissions from the South Stack will be in line with the requirements of Schedule 3, Table S3.1 of the existing Permit. Depending on the substance, monitoring of emissions to air will either be undertaken continuously by MCERTS certified Continuous Emissions Monitoring system (CEMS) equipment or by periodic extractive monitoring by MCERTs accredited contractors.

The Multifuel facility will continue to comply with the emission limits specified in the Permit.

The changes to the existing Permit as a result of this variation application will not lead to any changes in the monitoring requirements for the Multifuel facility.

6.3 Emissions to Sewer No changes are proposed to the emission limits contained in the existing Trade Effluent Discharge Consent for discharges to sewer from the Multifuel facility. As such, there will be no change in the composition or volume of emissions to sewer from the Multifuel facility from those proposed in the 2014 Permit Variation.

6.4 Emissions to Water As no additional emissions to water are proposed by this variation application, therefore, it is proposed that the limits and monitoring requirements in the current Permit (Table S3.2, Schedule 3) continue to apply to the Multifuel facility.

6.5 Monitoring of Process Variables Monitoring of process variables is covered under Table S3.4 in Schedule 3 of the existing Permit. The processes at the installation will not be altered by this variation application, therefore, it is proposed that the current monitoring regime for process variables continue to apply to the Multifuel facility.

Environmental Risk Assessment (Impact Assessment)

7.1 Introduction An assessment of the risk posed to the environment from emissions from the normal operation of the Multifuel facility and foreseen abnormal operations was undertaken as part of the 2014 Permit Variation (Annex 4 of the Supporting Document), based on maximum throughput of up to 480,000tpa of RDF in the Multifuel facility. Since the environmental risk assessment was based on the higher volume of RDF proposed to be treated at the Multifuel facility, no additional risk assessment has been undertaken.

An air quality impact assessment has been undertaken for the higher fuel throughput at the lowest NCV to support this variation application (Appendix B). A summary of the site location and sensitive receptors in the vicinity of the installation, which were considered within the assessment, is provided below.

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7.2 Site Location and Sensitive Receptors

7.2.1 Human Receptors The closest residential properties (individual receptors) are located approximately 200m to the North of the Multifuel facility. These are the residential properties on Bodmin Avenue. There are several other residences within 2km.

Table 7-1 below lists the human receptors in the vicinity of the installation.

Table 7-1: Human Receptors in the Vicinity of the Installation

Distance and Direction ID Description Type of Receptor from Site (km) R1 Bodmin Avenue Residential 0.2km North R2 Birch Grove Residential 0.5km Northeast R3 Farnburn Avenue Residential 0.6km Northeast R4 Melbourne Avenue Residential 1km East R5 Cippenham Lane Residential 0.6km Southwest R6 Greystoke Road Residential 0.8km Northwest R7 Tuns Lane AQMA3 1.4km Southeast R8 Town Centre AQMA4 2km Southeast

Figure 3.1 of the Air Quality Assessment (Appendix B) shows the locations of the sensitive human health receptors in the vicinity of the installation.

7.2.2 Sensitive Environmental Habitats The specific ecological receptors included in the dispersion modelling assessment are those located within the appropriate screening distances detailed in the EA’s Risk Assessment Guidance of 10km for internationally designated sites (i.e. Special Areas of Conservation (SACs), Special Protection Areas (SPAs) and Ramsar sites, and also nationally designated sites (i.e. Site of Special Scientific Interest (SSSIs), as per the 2014 Permit Variation assessment. In addition, locally designated sites (i.e. Local Wildlife Sites and Local Nature Reserves (LWS and LNRs) within 2km have also been considered. All habitat receptors are shown in Figure 3.2 of the Air Quality Assessment (Appendix B).

European designated sites up to 10km from the installation are listed in Table 7-2.

Table 7-2: Designated European Ecological Receptors in the Vicinity of the Site (within 10 km)

ID Receptor Designation Distance and Direction from Site

E1 Burnham Beeches SSSI, SAC 2.9km North E2 Stoke Common SSSI 4.3km North E3 South Lodge Pit SSSI 4.7km West E4 Bray Pennyroyal Field SSSI 4.9km Southwest E5 Littleworth Common SSSI 4.8km Northwest E6 Bray Meadows SSSI 5.6km West E7 Windsor Forest and Great Park SSSI, SAC 6.0km Southwest E8 Black Park SSSI 6.2km Northeast E9 Cannoncourt Farm Pit SSSI 7.6km Northwest E10 Wraysbury No. 1 Gravel Pit SSSI 7.8km Southeast E11 Cock Marsh SSSI 8.2km Northwest

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ID Receptor Designation Distance and Direction from Site

E12 Kingcup Meadows and Oldhouse Wood SSSI 8.2km Northeast E13 Great Thrift Wood SSSI 8.5km Southwest E14 South West London Waterbodies Ramsar 8.5km Southeast E15 Wraysbury and Hythe End Gravel Pits SSSI 9.1km South E16 Chawridge Bourne SSSI 9.4km Southwest E17 Bisham Woods and Chiltern Beechwoods SSSI, SAC 9.6km Northwest E18 Old Rectory Meadows SSSI 9.8km Northeast E19 Haymill Valley LNR 840m West E20 Cockersherd Wood LNR 1.4km Northwest

7.2.3 Hydrology The River Thames is located approximately 4km South of the installation boundary.

Two balancing ponds are situated external to the Multifuel facility where much of the surface water runoff from the Trading Estate flows into; one at Farnham Road and the other at Woodland Avenue. The water from the balancing ponds is then discharged into Salt Hill Stream and finally into the River Thames.

7.2.4 Geology The installation is underlain by a bedrock geology comprising clay, silt and sand of the Lambeth Group. The superficial geology of the installation comprises clay and silt.

7.2.5 Hydrogeology Available Defra maps8 show that the installation lies within designated Source Protection Zone 3. This is the area around a supply source within which all the groundwater ends up at the abstraction point. This is the point from where the water is taken. This could extend some distance from the source point.

The bedrock underlying the installation is identified to be located on a Secondary A aquifer (formerly classified as minor aquifers) which is defined by the EA as permeable layers capable of supporting water supplies at a local rather than strategic scale, and in some cases forming an important source of base flow to rivers. The superficial deposit underneath the installation is classified as unproductive strata which are rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow.

7.2.6 Pathways for Pollution In order for a pollution risk to occur, there has to be a source – pathway – receptor (S-P-R) linkage.

Pathways to sensitive receptors primarily include, but are not limited to:

· Fuel (RDF), chemicals and lubricating oil required for the operation of the Multifuel facility potentially leaching into the ground or being washed into surface water or groundwater through the underlying soils; · Combustion gases from the Multifuel facility dispersed into the air; and · Fugitive releases of particulates, odour and noise to air. In order to prevent and minimise the risk of pollution, the Multifuel facility has been designed and managed to isolate these pathways, preventing contaminants from migrating off-site other than through properly managed abatement systems.

8 DEFRA MAGIC mapping, available at https://magic.defra.gov.uk/MagicMap.aspx accessed on 29/10/2018

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Since the Multifuel facility was designed in consideration of the higher fuel throughput being proposed by this variation application, the pathways for accidental loss of fuel and chemicals were addressed in the 2014 Permit Variation. Furthermore, abatement measures for managing emissions to air from the facility will remain the same as proposed by the 2014 Permit Variation.

An additional air quality impact assessment, to demonstrate the impact on sensitive receptors due to the higher fuel throughput proposed by this variation application, has been carried out and is provided in Appendix B. Mitigation measures for minimising emissions to air from the facility are summarised in Section 4.2.

7.3 Impact Assessment The following sections provide an assessment of the impact of releases from the Multifuel facility, so as to underpin and justify the measures that will be put in place for their control and that will adequately protect the environment.

The risk assessment approach has been based on the following sequential stages:

· Identify risks from the activity; · Assess the risks and check that they are acceptable; · Justify appropriate measures to control the risks, if necessary; and · Present the assessment as detailed in the EA’s Risk Assessment Guidance9. Activities with the potential to impact on the surrounding environment have been identified in line with guidance provided in the EA’s Risk Assessment Guidance, including:

· Amenity and accidents; · Emissions to surface water; · Emissions to air; · Waste; · Global warming potential; and · Emissions to groundwater.

7.3.1 Amenity and Accidents A qualitative risk assessment was undertaken for the Multifuel facility and was included in the Environmental Risk Assessment10 (ERA) in Annex 4 of the 2014 Permit Variation. The risks assessed in the ERA were based on the maximum throughput of 480,000 tpa of RDF; therefore, it is considered that additional assessment for this application is not required. However, a reference and summary of the result of the original ERA has been provided in the following sections for completeness.

Noise and Vibration Table A2 of the ERA presented the noise risk assessment and management plan to be put in place for the Multifuel facility. The noise assessment reviewed the impact from the operation of the Multifuel facility and was based on the design of the Multifuel facility having a maximum throughput of 480,000tpa of RDF. It is therefore considered that the outcome of the noise assessment undertaken as part of the 2014 Permit Variation, i.e. impact of noise emissions from the Multifuel facility on NSRs not being significant, remains applicable.

Visible Plumes 7.3.1.2.1 Visibility of Plume from Main Stacks An assessment of the visible plume associated with the operational Multifuel facility was carried out as part of the 2014 Permit Variation, and it predicted that the visible plume effects from the twin line plant

9 https://www.gov.uk/government/collections/risk-assessments-for-specific-activities-environmental-permits, accessed on 10/10/2018 10 Slough Multifuel - Environmental Risk Assessment, document reference: S1515-0500-0006JRS, Fichtner Consulting Engineers Ltd for SHP Ltd, 11/12/2014

Prepared for: Slough Heat and Power Limited AECOM 18 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005 would be considered to be of “medium” significance in terms of the EA’s original version of the IPPC H1 Environmental Assessment Guidance Note from 2001.

The WI BREF states that plume visibility can be greatly reduced by maintaining stack release temperatures above 140°C, and the current design intention for the Multifuel facility is a minimum of 150°C.

The proposed twin line plant technology now has a lower water content in the stack gas (for both the design fuel and the lower NCV fuel) and the release temperature has increased from 140°C in the 2014 Permit Variation assessment to 150°C now. Therefore, it is considered that both these parameters will reduce the potential for visible plumes to occur from the Multifuel facility, based on the assessment carried out for 2014 Permit Variation assessment. No further assessment has therefore been deemed necessary for this variation application.

Accidents Table A4 of the ERA (Annex 4 of the Supporting Document of the 2014 Permit Variation) provides the details of accidents risk assessment and management plan for the Multifuel facility. Abnormal emissions were addressed in Annex 5 of the Supporting Document of the 2014 Permit Variation; the abnormal emissions from the Multifuel facility will not be affected by the variation proposed by this application.

An Accident Management Plan was submitted to the EA for completion of IC4 of the existing Permit.

A Fire Prevention Plan has been prepared for the Multifuel facility in response to IC23 of the existing Permit.

It is considered that this variation will not result in additional accident risk from the Multifuel facility operations.

7.3.2 Point Source Emissions to Water There will not be any direct discharges to the ground/ groundwater of process water from the activities proposed by this variation application. Section 6.2 and Table A4 of the ERA undertaken as part of the 2014 Permit Variation address potential emissions to controlled waters from the site operations, and it was considered that all process water will be managed appropriately, with appropriate segregation of surface water to prevent contamination. SHP will ensure all management procedures are followed and reviewed periodically, as required.

7.3.3 Point Source Emissions to Air The air quality assessment for the Multifuel facility is provided in Appendix B.

This assessment has been updated from the 2014 assessment to reflect the maximum fuel throughput of the Multifuel Facility (480,000 tpa at a fuel NCV of 10.5MJ/kg) and also to incorporate updates on the data available in relation to the predicted emissions associated with the specific combustion technology which has now been selected and is proposed to be installed (twin line plant from HZI). The ambient background and receptor data have also been updated to reflect current data available.

The air dispersion modelling exercise has been undertaken to assess the impact on local air quality as a result of the anticipated emission levels identified in the WI BRef (2006) and the IED, as shown in Table 5-3 and the key findings are summarised below.

Impact on Local Air Quality The Multifuel facility has been designed such that combustion plant emissions to air comply with the emission requirements specified in the WI-BRef (i.e. BAT-AELs).

An air quality impact assessment has been carried out for the Multifuel facility, with reference to the EA Risk Assessment methodology for Environmental Permitting.

Detailed dispersion modelling has been used to calculate the concentration of pollutants at identified sensitive receptors and these have been compared with National Air Quality Strategy (NAQS) objectives and Environmental Assessment Levels (EALs) for human health receptors and Critical Levels and Critical Loads for ecosystem receptors, with consideration for the baseline air quality and ecological deposition rates, in accordance with EA methodology.

Prepared for: Slough Heat and Power Limited AECOM 19 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

The assessment has been based on the worst-case operational scenarios with respect to potential air quality impacts, employing operational design parameters for the Multifuel facility. The assessment for Environmental Permitting compliance has been based upon the predicted maximum off-site impacts (beyond the Installation boundary), in order to carry out a worst-case assessment for human health impacts.

A number of other conservative assumptions have been made in combination, including:

· Use of the worst-case year of meteorological data modelled; · Use of maximum building sizes within the design; · The operation of the plant at 2006 WI-BRef emission limits; and · Conservative estimates of background concentrations of pollutants at the sensitive receptors. Detailed Dispersion Modelling Results The anticipated impacts on air quality resulting from the emissions to air from the Multifuel facility’s point source have been assessed using the screening criteria detailed in the Environment Agency’s (EA) Air Emissions Risk Assessment for your Environmental Permit guidance11, in order to screen out pollutant impacts that can be considered to be insignificant and do not require further investigation.

Pollutant species that require further assessment have been assessed through detailed dispersion modelling, using the proprietary model ADMS (version 5.5.2).

The maximum impact of the Multifuel facility’s point source emissions has been determined from isopleth figures of pollutant dispersion and the model output has also been determined at discrete receptor locations.

The results have been compared to those presented in the 2014 Permit Variation, and for all pollutant species, the process contributions at receptors are lower than those presented in the 2014 assessment. This is largely due to the higher release temperature and efflux velocity associated with the selected combustion technology design for the Multifuel facility.

It is therefore considered that the increased throughput resulting from the lower NCV fuel would not lead to a worsening of the environmental impacts associated with the permitted installation.

Habitats Assessment The impact of emissions of NOx, sulphur dioxide, ammonia and hydrogen fluoride have been assessed through comparison of the maximum predicted process contributions, at the identified sensitive sites. Again, the selected combustion technology design for the Multifuel facility results in a decrease in the predicted impacts when compared to the original 2014 Permit Variation assessment.

7.3.3.3.1 Deposition Impacts - Nutrient Nitrogen and Acid Due to the lower predicted annual average impacts at the identified ecological receptors for the revised assessment, it has not been considered necessary to fully revise the nutrient nitrogen or acid depositional impacts from the 2014 Permit Variation, although a comparison of the worst impacted site has been made for the new proposed plant and the 2014 Permit Variation results.

7.3.4 Conclusion It is therefore considered that the impact of the proposed Multifuel operations will not lead to a significant impact on the sensitive receptors (both human and ecological) in the vicinity of the installation.

7.4 Site Waste The key waste generated by the proposed activities will include bottom ash and APC residue, in addition to small quantities of general waste from the office and maintenance. The anticipated volumes of waste for the revised fuel throughput of 480,000tpa are shown in Table 4-1.

The waste management routes described in the 2014 Permit Variation are remain valid for this variation application.

11 https://www.gov.uk/guidance/air-emissions-risk-assessment-for-your-environmental-permit accessed 14/11/2019.

Prepared for: Slough Heat and Power Limited AECOM 20 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

It is therefore considered that the management procedures for the wastes arising from the Multifuel facility are appropriate, and further assessment of the waste from the proposed operations is not required.

7.5 Global Warming Potential (GWP) A Greenhouse Gas Assessment12 (GGA) was prepared for the Multifuel facility as part of the 2014 Permit Variation on the basis of generation of 50MW of electrical energy and 20MW of thermal energy. This application does not propose any changes in the electrical and thermal outputs from Multifuel facility, or the range of waste fuel calorific values permitted and therefore the impact of greenhouse gas emissions from the facility and the conclusions of the GGA carried out in 2014 are considered to remain valid.

7.6 Abnormal Operations An assessment of potential abnormal operational conditions resulting in significant emissions13 was undertaken as part of the 2014 Permit Variation. Due to the highly conservative nature of the assessment and the assessment being based on the maximum throughput of 480,000tpa of fuel to the Multifuel facility, it is considered that the scale and impact of potential abnormal operating conditions at the Multifuel facility have been addressed adequately. Additional consideration to abnormal operations or associated emissions has therefore not been carried out for the purpose of this variation application.

Closure and Decommissioning

This application does not propose any amendment to the design and operating life of the Multifuel facility, as outlined in Section 2.9 of the Supporting Information of the 2014 Permit Variation. A site closure plan has been developed for the installation, as required by IC12 within the existing Permit. Prior to the commencement of operation this will updated to include the Multifuel facility.

As the 2014 Permit Variation was based on the RDF throughputs proposed by this application, and no new infrastructure or associate plant and equipment is proposed to be added to the facility in this application, it is considered that the closure plan as outlined in the 2014 Permit Variation continues to apply to the Multifuel facility.

12 Slough Multifuel - GHG Assessment Report, document reference: S1515-0500-0009JFP, Fichtner Consulting Engineers Ltd for SHP Ltd, 11/12/2014 13 Slough Multifuel - Abnormal Emissions Assessment, document reference: S1515-0500-0011RSS, Fichtner Consulting Engineers Ltd for SHP Ltd, 04/12/2014

Prepared for: Slough Heat and Power Limited AECOM 21 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Appendices

Prepared for: Slough Heat and Power Limited AECOM Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Appendix A - Figures

Figure 1: Site Location

Figure 2: Installation Layout and Boundary

Prepared for: Slough Heat and Power Limited AECOM THIS DRAWING IS TO BE USED ONLY FOR THE PURPOSE OF ISSUE THAT IT WAS ISSUED FOR AND IS SUBJECT TO AMENDMENT

LEGEND ^_ Site Location d x m . 1 v _ n a l P _ n Copyright o i t a _ c ^ R eproduced from Ordnance Survey digital map data o L

_ © Crown copyright 2020. All rights reserved. e t i

S Licence number 0100031673. _ 1 \ s e r u g i F \ 9 1 0 2 n o i t a i r a V t i Purpose of Issue m r e

P ENVIRONMENTAL PERMIT

W f

E VARIATION APPLICATION h g Client u o l S

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S SLOUGH HEAT AND POWER LTD S \ X _ a e r Project Title A l a c i n h c e SLOUGH HEAT AND POWER T _ 0

3 STATION - MULTIFUEL FACILITY 4 \ l a c i n h c e

T Application Document Ref _ 0 0 4 \ h g u o l S _ SITE LOCATION PLAN E S S _ 2 2 5 3 2

3 Drawn Checked Approved Date - R

P LC AS AS 21/02/20 \ s b o AECOM Internal Project No. Scale @ A3 J \ 2

S 60578218 1:10,000 D L

K THIS DOCUMENT HAS BEEN PREPARED PURSUANT TO AND SUBJECT TO THE

U TERMS OF AECOM'S APPOINTMENT BY ITS CLIENT. AECOM ACCEPTS NO LIABILITY \ I FOR ANY USE OF THIS DOCUMENT OTHER THAN BY ITS ORIGINAL CLIENT OR K

U FOLLOWING AECOM'S EXPRESS AGREEMENT TO SUCH USE, AND ONLY FOR THE \ a i PURPOSES FOR WHICH IT WAS PREPARED AND PROVIDED. m e \ AECOM m o One Trinity Gardens c . t Quayside e n Newcastle upon Tyne m

o NE1 2HF c e T +44 (0)191 224 6500 a . www.aecom.com u e \ \ : 0 200 400 600 800 1,000 Drawing Ref Rev e m a Meters N e l FIGURE 1 i ± F THIS DRAWING IS TO BE USED ONLY FOR THE PURPOSE OF ISSUE THAT IT WAS ISSUED FOR AND IS SUBJECT TO AMENDMENT

LEGEND S5 ! Installation Boundary Water Treatment Plant (WTP) ! Emission Point

WEST EAST COOLING COOLING TOWER TOWER

S4 ! W1 ! W2 !

NORTH STACK !EXISTING NORTH STACK

BO ILER 17 STAFF FACILITIES & WORKSHOP 342 TURBINE HOUSE

TURBINE HALL

N d e w W x e ighb m rid

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e e g r 2 n u i t v t c s i _ Copyright u t x r t E u S o 6 No. SHELTERED CYCLE

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_ WTP Transformer 2 \ s e r

u Switch Gear g i & DNO room F \ 9 s 1 e 0 c 2 a

p n S o i r t a a i C r

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Purpose of Issue b TREATMENT . m h o r g i N e e 1 P 2 ENVIRONMENTAL PERMIT W

g W f n i t E

s VARIATION APPLICATION i h x g E Client u SOUTH STACK BO ILER HALL WASTE BUNKER TIPPING HALL o l NEW SOUTH S

STACK

E !

S SLOUGH HEAT AND POWER LTD S \ X _ a e r Project Title A l a c i n h c e SLOUGH HEAT AND POWER T _ 0

3 STATION - MULTIFUEL FACILITY 4

\ RO l a c i lant n P h c e

T Application Document Ref _ S2 S1

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4 UP \ ! h ! g u o l S _ SITE LAYOUT PLAN E S S _ 2 2 5 3

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P LC AS HW 01/04/20 \ s b o AECOM Internal Project No. Scale @ A3 J \ PACKAGE BOILER STACK 2

S 60578218 NTS D

L !

K THIS DOCUMENT HAS BEEN PREPARED PURSUANT TO AND SUBJECT TO THE PACKAGE BO ILER U TERMS OF AECOM'S APPOINTMENT BY ITS CLIENT. AECOM ACCEPTS NO LIABILITY \ I FOR ANY USE OF THIS DOCUMENT OTHER THAN BY ITS ORIGINAL CLIENT OR K

U FOLLOWING AECOM'S EXPRESS AGREEMENT TO SUCH USE, AND ONLY FOR THE \ a i PURPOSES FOR WHICH IT WAS PREPARED AND PROVIDED. m e \ AECOM m S3 o One Trinity Gardens c . t Quayside e ! n Newcastle upon Tyne m

o NE1 2HF c e T +44 (0)191 224 6500 a . www.aecom.com u e \ \ : Drawing Ref Rev e m a N e l FIGURE 2 i ± F Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Appendix B – Air Quality Impact Assessment

Prepared for: Slough Heat and Power Limited AECOM

Appendix B - Air Quality Assessment

Environmental Permit Variation Application Slough Heat and Power Station

Slough Heat and Power Limited

Project reference: 60578218 Project number: 60578218.005 60578218-ACM-PM-RP-EN-001-A

14 April 2020

Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Quality information

Prepared by Verified by Approved by Helen Watson Garry Gray Mark Webb Associate Associate Director Technical Director

Revision History

Revision Revision date Details Authorized Name Position Initial draft 10/03/2020 Client review Helen Watson Helen Watson Project Manager Final 14/04/2020 Final for issue Helen Watson Helen Watson Project Manager

Prepared for: Slough Heat and Power Limited AECOM Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Prepared for: Slough Heat and Power Limited Andrew Ellis 342 Edinburgh Avenue Slough SL1 4TU

Prepared by: Helen Watson Associate T: 07759 237570 E: [email protected]

AECOM Infrastructure & Environment UK Limited 5th Floor, 2 City Walk Leeds LS11 9AR United Kingdom

T: +44 (0)113 391 6800 aecom.com

© 2020 AECOM Infrastructure & Environment UK Limited. All Rights Reserved.

This document has been prepared by AECOM Infrastructure & Environment UK Limited (“AECOM”) for sole use of our client (the “Client”) in accordance with generally accepted consultancy principles, the budget for fees and the terms of reference agreed between AECOM and the Client. Any information provided by third parties and referred to herein has not been checked or verified by AECOM, unless otherwise expressly stated in the document. No third party may rely upon this document without the prior and express written agreement of AECOM.

Prepared for: Slough Heat and Power Limited AECOM Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Table of Contents

Introduction...... 1 Assessment Criteria ...... 1 2.1 Environmental Standards ...... 1 2.2 Background Concentrations ...... 3 2.2.1 Slough Borough Council’s Monitoring Data...... 3 2.2.2 Defra Background Maps and Monitoring Data ...... 4 2.2.3 Background Data at Habitat Sites...... 5 2.2.4 Air Quality Management Areas ...... 5 2.3 Assessment Significance Criteria ...... 5 2.3.1 Human Health Significance Criteria ...... 5 2.3.2 Protected Conservation Areas Significance Criteria ...... 5 Dispersion Modelling ...... 6 3.1 Introduction ...... 6 3.2 Emission Parameters ...... 6 3.3 Modelling Domain and Sensitive Receptors ...... 9 3.4 Meteorology ...... 13 3.5 Building and Terrain Effects ...... 15 Predicted Results...... 16 Conclusions ...... 26 Annex A – Sensitivity Assessment ...... 29 Annex B – Isopleth Figures ...... 30

Tables

Table 2.1: Environmental Standards Applicable to the Assessment ...... 2 Table 2.2: SBC Salt Hill Continuous Monitoring Data ...... 3 Table 2.3: Defra Background Concentrations - 2019 ...... 4 Table 2.4: Heavy Metals Background Monitoring Data...... 4 Table 3.1: Emission Parameters Modelled for the 2014 Permit Variation, and the Proposed Plant ...... 7 Table 3.2: Identified Receptors in the Installation Vicinity ...... 10 Table 3.3: Modelled Building Parameters ...... 15 Table 4.1: Comparison of the 2014 Permit Variation Results and the Proposed Plant (based on 2008 meteorological data) ...... 17 Table 4.2: Comparison of the 2014 Permit Variation Results and the Proposed Plant (worst case new meteorological data 2014 - 2018) ...... 20 Table 4.3: Model Results for the Proposed Plant at the Lower NCV Fuel – Human Health Impacts (worst case new meteorological data 2014 - 2018)...... 23 Table 4.4: Model Results for the New Proposed Plant at the Lower NCV Fuel – Ecological Impacts (worst case new meteorological data 2014 - 2018)...... 25 Table 4.5: N-Deposition Impacts Compared for the 2014 Variation (2008 meteorological data) and the Revised Assessment (worst case new meteorological data 2014 - 2018) ...... 26

Prepared for: Slough Heat and Power Limited AECOM Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Introduction

This impact assessment has been prepared by AECOM Limited (“AECOM”) on behalf of Slough Heat and Power Limited (“SHP”) to assess the potential environmental impacts of an increase in fuel throughput and lower Net Calorific Value (NCV) for the Multifuel facility at the Slough Heat and Power Station (“SHPS” or the “installation”). This assessment has been prepared in order to support the Environmental Permit variation application for the increased fuel throughput.

The Environmental Permit for the Multifuel facility at the SHPS currently allows a Refuse Derived Fuel (RDF) throughput of 438,000 tonnes per annum (tpa), which was based on the design fuel at the time of the original Environmental Statement and Environmental Permit Variation application submitted in September 2014 and December 2014 (“2014 Permit Variation”) respectively. Now the design of the Multifuel plant has been finalised, SHP are looking to vary their Environmental Permit to increase the RDF tonnage of the Multifuel facility to 480,000 tpa, based on the potential use of a lower NCV fuel. A review of the emission parameters associated with the lower NCV fuel compared to those assessed for the 2014 Permit Variation, has been carried out and is reported in this Appendix. In addition, the actual design data for the proposed technology for the twin line plant (supplied by HZI) at the lower design NCV, is now available and therefore this has been modelled to determine whether there are any changes to the predicted impacts from the Multifuel facility, compared to the 2014 Permit Variation. As such, this assessment is only concerned with emissions from the Multifuel plant, to enable comparison with the assessment carried out for the 2014 Permit Variation. It is considered that other existing site emissions are included within the background concentrations used within the assessment. The anticipated impacts on air quality resulting from the emissions to air from the Multifuel facility’s point source have been assessed using the screening criteria detailed in the Environment Agency’s (EA) Air Emissions Risk Assessment for your Environmental Permit guidance1, in order to screen out pollutant impacts that can be considered to be insignificant and do not require further investigation.

Pollutant species that require further assessment have been assessed through detailed dispersion modelling, using the proprietary model ADMS (version 5.5.2). Emissions to air from the Multifuel facility’s point source have been modelled to determine the likely worst-case Process Contributions (PCs). These have been added to the background pollutant concentrations (BC) to determine the overall Predicted Environmental Concentration (PEC) at sensitive receptor locations, which have then been assessed against air quality standards.

An assessment of the potential impacts on residential receptors in the locality as well as sensitive Habitat sites, has also been undertaken.

Assessment Criteria

2.1 Environmental Standards The principal air quality legislation within the United Kingdom (UK) is the Air Quality Standards Regulations 2010, which transposes the requirements of the European Ambient Air Quality Directive 2008 (European Commission, 2008) and the 2004 fourth Air Quality Daughter Directive (European Commission, 2004). The Regulations set air quality limits for a number of major air pollutants that have the potential to impact public health, such as nitrogen dioxide (NO2), particulate matter (PM10), sulphur dioxide (SO2) and Carbon Monoxide (CO), which are emitted from the Multifuel facility.

The Environment Act 1995 requires the UK Government to produce a national air quality strategy (NAQS), last reviewed in 2007 (Department for Environment, Food and Rural Affairs (Defra)), containing air quality objectives and timescales to meet those objectives. These objectives apply to outdoor locations where people are regularly present and do not apply to occupational, indoor or in-vehicle exposure.

1 https://www.gov.uk/guidance/air-emissions-risk-assessment-for-your-environmental-permit accessed 14/11/2019.

Prepared for: Slough Heat and Power Limited AECOM 1 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

The NAQS also defines Critical Levels for the protection of vegetation and ecosystems (CLs) for oxides of nitrogen for the protection of sensitive ecological receptors. The term “Critical Levels” (CLs) refers to the concentrations of a pollutant in the atmosphere above which adverse effects on receptors, such as plants and/ or ecosystems may occur.

In addition, the Environment Agency (EA) has defined Environmental Assessment Levels (EALs) for the protection of human heath for pollutant species without NAQS objectives, such as hydrogen chloride and hydrogen fluoride and various metals. They have also defined an additional hourly Environmental Assessment Level (EAL) for human heath for CO.

Table 2.1 shows the current NAQS objectives, EALs and CLs (hereon in collectively referred to as “Environmental Standards”) applicable to this assessment.

Table 2.1: Environmental Standards Applicable to the Assessment

NAQS Objectives/ EALs/ CLs Pollutant Limit Averaging Period 1-hour mean, not to be exceeded more than 18 200 Nitrogen Dioxide times per year (NO ) 2 40 Annual mean Oxides of Nitrogen 75v Daily mean (NOx) 30v Annual mean 15-min mean, not be exceeded more than 35 266 times a year 1-hour mean, not to be exceeded more than 24- 350 Sulphur Dioxide times a year (SO2) 24-hour mean, not to be exceeded more than 3 125 times a year 20v Annual mean Daily mean – not to be exceeded more than 35 50 Particulate Matter times a year (PM10) 40 Annual mean

(PM2.5) 20 Annual mean

10,000 Maximum daily running 8-hour mean Carbon Monoxide (CO) 30,000 Hourly mean (100th percentile)

Lead (Pb) 0.25 Annual mean 16.25 Running annual mean Benzene 5.0 Annual mean Polycyclic Aromatic Hydrocarbons 0.25ng/m3 Annual mean (PAH) Hydrogen Chloride 750 Hourly 100th percentile (HCl) 160 Hourly 100th percentile Hydrogen Fluoride 16 Annual mean (HF) 5v Daily mean 0.5 Weekly mean Cadmium (Cd) 0.005 Annual mean Arsenic (As) 0.006 Annual mean Lead (Pb) 0.25 Annual mean 7.5 1 hour 100th percentile Mercury (Hg) 0.25 Annual mean

Prepared for: Slough Heat and Power Limited AECOM 2 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

NAQS Objectives/ EALs/ CLs Pollutant Limit Averaging Period 11 1 hour 100th percentile Other Metals 0.152 Annual mean 2,500 1 hour 100th percentile

NH3 180 Annual mean 3v Annual mean (higher plants) V For the protection of vegetation and ecosystems. Other standards are for the protection of human health. 1 EAL for vanadium taken as the worst case for all other heavy metals. 2 EAL for manganese taken as the worst case for all other heavy metals.

Since the emissions from the installation are mixed into the ambient air, an assessment must also include the contribution to pollutant levels from other sources, which is derived from the ambient background concentrations. The Process Contribution (PC) must therefore be added to an appropriate Ambient Concentration (AC) to give the total Predicted Environmental Concentration (PEC). It is the PEC that is compared with the appropriate Environmental Standard to ensure that air quality is not being significantly affected.

2.2 Background Concentrations As the emissions from the Multifuel facility will be mixed into the ambient air, an assessment must also include the contribution to pollutant levels from other sources, which is derived from the ambient background concentrations. The Process Contribution (PC) from the Installation must therefore be added to an appropriate Background Concentration (BC) to give the total Predicted Environmental Concentration (PEC). It is the PEC that is compared with the appropriate Environmental Standard to ensure that air quality is not being significantly affected.

Environmental Standards are set for both short- and long-term averaging periods. It is unrepresentative to add the worst case short-term PC to the worst case short-term AC since it is highly unlikely that the two will coincide at the same event. Therefore, the BC added to the short term PC is typically a multiple of the annual average concentration, rather than the short term ambient concentration over the equivalent averaging period.

The BCs in the vicinity of the Multifuel facility have been determined through a review of Slough Borough Council’s (SBC) local air quality management reports, and also a review of data held on the Defra background pollutant database2.

2.2.1 Slough Borough Council’s Monitoring Data

The ambient concentrations of NO2 and PM10 used in the 2014 Permit Variation assessment were taken from the Salt Hill A4 continuous monitor, maintained by SBC, for the year 2013. The data now available has been reviewed, and it is considered that this monitor remains the most representative of the background data in the vicinity of the Multifuel facility. The data has therefore been updated for this revised assessment and is present in Table 2.2, compared to the data used in the 2014 Permit Variation assessment.

Table 2.2: SBC Salt Hill Continuous Monitoring Data

2013 Location (as 2014 Permit 2018 Variation Nitrogen Dioxide (µg/m3) 35.8 31

3 PM10 (µg/m ) 21.6 16.9

It can be seen from Table 2.2, that the ambient concentrations of NO2 and PM10 measured at the Salt Hill continuous monitoring station have reduced since the time of the 2014 Permit Variation. This was predicted

2 https://uk-air.defra.gov.uk/data/laqm-background-home

Prepared for: Slough Heat and Power Limited AECOM 3 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005 in the original assessment, due to the general trend of reducing concentrations across the UK, as the older vehicle fleet is replaced with newer vehicles.

2.2.2 Defra Background Maps and Monitoring Data

Background concentrations of NO2, PM10, PM2.5, CO and SO2 at the Multifuel facility’s location have also been obtained from the Defra background pollutant database, in which pollutant concentrations are averaged over 1km x 1km grid basis across the UK. Data is available for 2019 for NO2, PM10, PM2.5, (from 2017 baseline maps) and is shown in Table 2.3.

Data for CO and SO2 has not been updated since the 2001 baseline maps and therefore these figures have been used, and where appropriate the year adjustment factor have been applied.

Table 2.3: Defra Background Concentrations - 2019

3 3 3 3 3 Location NO2 (µg/m ) PM10 (µg/m ) PM2.5 (µg/m ) CO (µg/m ) SO2 (µg/m ) Site 25.2 16.3 11.3 196 3.9 (NGR 495500, 181500)

The data from the Salt Hill monitoring station is higher than the Defra background map data and therefore this has been used for the assessment, in order that a conservative assessment is carried out.

Estimates for background concentrations of other study species have been obtained through the Defra UK Air Information Resource website, which provides data for various UK Monitoring Networks.

No additional data for background concentrations of HCl is available since the 2014 Permit Variation assessment, and therefore these are assumed to be the same as in that assessment at 0.35µg/m3. Background concentration of HF have been assessed at an annual average of 0.003µg/m3, based on information within the EP AQS report3.

Heavy metals data has been taken from the London Marylebone Road monitoring site (as the closest available site to Slough) and is shown in Table 2.4 for 2018.

Table 2.4: Heavy Metals Background Monitoring Data

2018 Annual Mean Pollutant Concentration (ng/m3) Arsenic 0.88 Cadmium 0.16 Chromium 8.8 Cobalt 0.22 Copper 53.8 Lead 6.7 Manganese 15.3 Nickel 1.7 Vanadium 1.0 Zinc 38.7

3 Defra, Scottish Executive, National Assembly of Wales and Department of the Environment in Northern Ireland. (2006). Guidelines for halogens and hydrogen halides in ambient air for protecting human health against acute irritancy effects.

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2.2.3 Background Data at Habitat Sites

Background NOx, SO2 and ammonia concentrations at the Habitat sites identified for the assessment have been obtained from the Air Pollution Information Service website4.

2.2.4 Air Quality Management Areas SBC have declared five Air Quality Management Areas (AQMAs) within Slough due to breaches of the annual mean concentrations for NO2, associated with traffic emissions. These are:

· AQMA 1 – Land adjacent to the M4 between junctions 5-7; · AQMA 2 - A4 London Road east of junction 5 of the M4; · AQMA 3 - A355 Tuns Lane from junction 6 of the M4 motorway; · AQMA 4 - A4 Bath Road from the junction with Ledgers Road/ Stoke Poges Lane; and, · AQMA 3 - Extended to the stretch of road between Tuns Lane Junction known as the “Three Tuns” and 30 Bath Road. The closest AQMA to the facility is the AQMA 3, which is approximately 1.4m to the southeast of the Multifuel facility. Given the prevailing wind direction (originating from the south-west), it is considered unlikely that the emissions from the Multifuel facility would contribute to exceedances within these AQMAs, which are principally designated as a result of the contribution from traffic emissions, however the impact on these areas has been determined, where necessary for the purpose of assessment, and the BCs of NO2 at these receptors has been determined from Defra Background maps and Slough Borough Council’s 2019 Air Quality Annual Status Report5, as appropriate.

2.3 Assessment Significance Criteria According to the EA’s Risk Assessment Guidance methodology, it is possible to identify emissions that result in “insignificant” impacts and those emissions where further assessment is not required, based on the contribution to the appropriate Environmental Standard for each pollutant.

2.3.1 Human Health Significance Criteria The EA’s Risk Assessment screening criteria for significance of the emissions have been applied to the outcome of the dispersion modelling. The predicted PCs have been compared with the appropriate Environmental Standard to determine the significance of the pollutant emission.

The total pollutant emission is defined in the EA’s Risk Assessment guidance as having an insignificant impact where:

─ PC <1% of the Environmental Standard, or the PEC <70% of the Environmental Standard for long term releases; ─ PC <10% of the Environmental Standard, or the PC is less than 20% of the Environmental Standard minus twice the long term background concentration, for short term releases.

2.3.2 Protected Conservation Areas Significance Criteria The EA’s Risk Assessment guidance screening criteria for significance of the emission have been applied to the outcome of the dispersion modelling for both European sites and SSSIs. The predicted PCs have been compared with the appropriate Critical Level to determine the significance of the effect of the predicted PC.

The total pollutant emission is defined in the EA’s Risk Assessment guidance as being insignificant where:

─ PC <1% of the Critical Level, or the PEC <70% of Critical Level for long term releases; ─ PC <10% of the Critical Level for short term releases.

4 www.apis.ac.uk 5 Slough Borough Council. (2019). Annual Status Report 2019.

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Dispersion Modelling

3.1 Introduction Detailed dispersion modelling using the atmospheric dispersion model ADMS (version 5.2.2) has been used to calculate the concentrations of released pollutants (the PC) from the Multifuel facility. These concentrations have been compared with the relevant Environmental Standard for each pollutant species released.

The degree of turbulence in the atmosphere affects the rate at which pollutants from point sources are dispersed in the environment. The more unstable the atmosphere – for example due to high solar insolation – the greater the degree of mixing. While this is in principle the desired effect for the release of pollutants through stacks at elevated heights, this can also lead to localised peak concentrations if the plume is rapidly brought to ground level.

Various parameters can affect the degree of dispersion from a source, and these are accounted for in the modelling scenario where appropriate, as detailed in the following sections. The presence of elevated or complex terrain in the vicinity of the source can affect the flow pattern of the wind field, which can in turn bring a plume to ground more rapidly. Buildings of sufficient height located close to the emission sources can affect dispersion – inducing downwash in the emitted plume and entraining pollutants towards ground level.

ADMS utilises site-specific hourly sequential meteorological data to enable a realistic assessment of dispersion from point sources to be conducted for weather conditions that are directly applicable to the site.

Sensitivity analysis of the model to a number of the input parameters, including the use of different meteorological years has been carried out and is detailed in Annex A.

The model parameters applied, are identical to those applied to the dispersion modelling carried out for the 2014 Permit Variation, however they have been specified again in this Appendix for ease of reference.

3.2 Emission Parameters At the time of the 2014 Permit Variation, the final technology supplier for the Multifuel facility had not been selected. The emissions modelled were therefore based on either a single or twin line plant, from data that had been provided by several potential technology providers. The data selected for inclusion in the dispersion modelling assessment was considered to represent the worst-case emission parameters from all the data that had been provided at that time.

Now that the design for the plant is more developed, data is available for the proposed twin line plant from the selected contractor, HZI. The emission parameters modelled for the 2014 Permit Variation are shown in Table 3.1, together with the parameters for the now proposed plant technology. Although included in Table 3.1 for completion (as at the time of the 2014 Permit Variation this was considered to lead to the worst-case impacts), the previously assessed single line plant data has been greyed out.

No assessment of dioxin, furan and PCB species have been carried out as part of this assessment, as these were assessed in full for the 2014 Permit Variation assessment. A generalised comparison of the results from the original assessment has been made to the results in this revised assessment, and is presented in Section 4.

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Table 3.1: Emission Parameters Modelled for the 2014 Permit Variation, and the Proposed Plant

Stack OS Grid Stack Stack Flow Flow Flow Efflux Daily Av Emission2 ½ Hourly Av Emission3 Temp Moisture Oxygen Coordinates Height Diameter Rate Rate Rate1 Velocity Scenario Pollutant Conc Release Conc Release x y (m) (m) °C % % Am3/s Am3/hr Nm3/s Am/s mg/m3 Rate g/s mg/m3 Rate g/s

NOx 200 13.05 400 26.11

SO2 50 3.26 200 13.05 TPM 10 0.65 30 1.96 Original CO 50 3.26 100 6.53 Single Line HCl 10 0.65 60 3.92 (NCV of 495271 181446 85 2.47 140 18.1 7.0 86.0 309,550 65.3 17.9 design fuel HF 1 0.065 4 0.26 12.06 MJ/kg) VOC4 10 0.65 20 1.31 Cd, Tl, Hg 0.05 0.0033 - - Other Metals5 0.5 0.033 - - 6 NH3 5 0.33 - -

NOx 200 18.54 400 37.09

SO2 50 4.64 200 18.54 TPM 10 0.93 30 2.78 Original Twin CO 50 4.64 100 9.27 Line (NCV of HCl 10 0.93 60 5.56 495262 181460 90 2.96 140 19.2 7.0 123.9 445,948 92.7 18.0 design fuel HF 1 0.093 4 0.37 12.06 4 MJ/kg) VOC 10 0.93 20 1.85 Cd, Tl, Hg 0.05 0.0046 - - Other Metals5 0.5 0.046 - - 6 NH3 5 0.46 - -

NOx 200 20.24 400 40.48

Proposed SO2 50 5.06 200 20.24 HZI Twin TPM 10 1.01 30 2.02 Line Plant (NCV of CO 50 5.06 100 15.18 design fuel HCl 10 1.01 60 6.07 12.06 495262 181460 90 2.68 150 20.5 6.0 131.5 473,289 102.2 23.3 MJ/kg) HF 1 0.10 4 0.40 Emission VOC4 10 1.01 20 2.02 Points - South Stack Cd, Tl, Hg 0.05 0.0051 - - 1 & 2 Other Metals5 0.5 0.051 - - 6 NH3 5 0.51 - -

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Stack OS Grid Stack Stack Flow Flow Flow Efflux Daily Av Emission2 ½ Hourly Av Emission3 Temp Moisture Oxygen Coordinates Height Diameter Rate Rate Rate1 Velocity Scenario Pollutant Conc Release Conc Release x y (m) (m) °C % % Am3/s Am3/hr Nm3/s Am/s mg/m3 Rate g/s mg/m3 Rate g/s

NOx 200 21.02 400 42.03

Proposed SO2 50 5.25 200 21.02 HZI Twin TPM 10 1.05 30 2.10 Line Plant (NCV of CO 50 5.25 100 15.76 proposed HCl 10 1.05 60 6.30 fuel 10.5 495262 181460 90 2.68 150 20.5 6.1 137.0 493,147 104.7 24.3 MJ/kg) HF 1 0.11 4 0.42 Emission VOC4 10 1.05 20 2.10 Points - Cd, Tl, Hg 0.05 0.0056 - - South Stack 1 & 2 Other Metals5 0.5 0.056 - - 6 NH3 5 0.56 - - 1 Normalised to 0ºC, 101kPa, Dry at 11% oxygen 2 Used for the assessment of annual average impacts. 3 Used for the assessment of short term impacts. 4 VOCs conservatively assumed to be 100% benzene. 5 Includes Sb, As, Pb, Cr, Co, Cu, Mn, Ni and V. 6 ELV for ammonia is a proposed ELV, and isn’t stipulated in the IED.

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It can be seen from Table 3.1 that the emissions of the proposed HZI twin line plant are released at a higher temperature and efflux velocity than those assessed for the 2014 Permit Variation. The normalised flow rate is higher than the 2014 Permit Variation assessment, resulting in higher mass emission rates than those previously assessed, for both the design fuel (12.06 MJ/kg) and the lower NCV fuel (10.5 MJ/kg).

It is therefore considered that, due to the higher temperature and efflux velocity, the resulting emissions will have improved thermal and momentive buoyancy than those assessed for the 2014 Permit Application, and that this will counter the potential increase in impacts that the higher mass release rates may cause.

Emissions of nitrogen oxides from industrial point sources are typically dominated by nitric oxide (NO), with emissions from combustion sources typically in the ratio of nitric oxide to nitrogen dioxide (NO2) of 9:1. However, it is NO2 that has specified NAQS objectives due to its potential impact on human health. In the ambient air, NO is oxidised to NO2 by the ozone present, and the rate of oxidation is dependent on the relative concentrations of NO and ozone in the ambient air

For the purposes of detailed modelling, and in accordance with the EA’s technical guidance6 it is assumed that 70% of emitted nitric oxide is oxidised to nitrogen dioxide in the long term and 35% of the emitted nitric oxide is oxidised to nitrogen dioxide in the local vicinity of the site in the short-term.

3.3 Modelling Domain and Sensitive Receptors The dispersion modelling has been carried out using a grid extending 2km x 2km from the Multifuel facility’s stack with grid points at 50m intervals. Specific receptor locations at the nearest identified residential properties to the Multifuel facility have also been included in the model and results at discrete receptors are unaffected by grid spacing.

The assessment for Environmental Permitting compliance has been based upon the predicted maximum off-site impacts (beyond the Installation boundary), in order to carry out a worst-case assessment for human health impacts. It can be seen from the contour (isopleth) plots provided in Annex B that maximum impacts are predicted to occur beyond the boundary, and therefore assessing the maximum off-site impacts is considered appropriate, particularly for short term impacts, where there is potential for human receptors to be within the vicinity of the Multifuel facility for short periods, such as at local recreational areas that may not have been identified as specified receptors. Impacts have also been determined at the worst case discrete residential receptor, where maximum off-site impacts have not been screened as insignificant. The process contribution of NO2 at the worst case AQMA has also been determined.

The specific human health receptors included in the dispersion modelling assessment are identified in Table 3.2, and their locations are shown in Figure 3.1.

The specific ecological receptors included in the dispersion modelling assessment are also identified in Table 3.2. These receptors are within the appropriate screening distances detailed in the EA’s Risk Assessment Guidance of 10km for internationally designated sites (i.e. Special Areas of Conservation (SACs), Special Protection Areas (SPAs) and Ramsar sites, and also nationally designated sites (i.e. Site of Special Scientific Interest (SSSIs), as per the 2014 Permit Application assessment. In addition, locally designated sites (i.e. Local Wildlife Sites and Local Nature Reserves (LWS and LNRs) within 2km have also been considered.

All habitat receptors are shown in Figure 3.2.

6 https://webarchive.nationalarchives.gov.uk/20140328232919/http://www.environment- agency.gov.uk/static/documents/Conversion_ratios_for__NOx_and_NO2_.pdf

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Table 3.2: Identified Receptors in the Installation Vicinity

Grid Reference Distance from Receptor Name Receptor Type (approx)1 Installation Boundary

R1 Bodmin Avenue Residential 495403, 181759 0.2km North

R2 Birch Grove Residential 495672, 181655 0.5km Northeast

R3 Farnburn Avenue Residential 495868, 181578 0.6km Northeast

R4 Melbourne Avenue Residential 496253, 181282 1km East

R5 Cippenham Lane Residential 494923, 180924 0.6km Southwest

R6 Greystoke Road Residential 494360, 181847 0.8km Northwest

R7 Tuns Lane AQMA3 496365, 180459 1.4km Southeast

R8 Town Centre AQMA4 496900, 180135 2km Southeast

E1 Burnham Beeches SSSI, SAC 495052, 184315 2.9km North

E2 Stoke Common SSSI 497931, 184870 4.3km North

E3 South Lodge Pit SSSI 490599, 181914 4.7km West

E4 Bray Pennyroyal Field SSSI 491562, 178312 4.9km Southwest

E5 Littleworth Common SSSI 493460, 185994 4.8km Northwest

E6 Bray Meadows SSSI 489823, 180293 5.6km West

E7 Windsor Forest and Great Park SSSI, SAC 495519, 175402 6.0km Southwest

E8 Black Park SSSI 500878, 184093 6.2km Northeast

E9 Cannoncourt Farm Pit SSSI 487860, 183012 7.6km Northwest

E10 Wraysbury No. 1 Gravel Pit SSSI 500253, 175441 7.8km Southeast

E11 Cock Marsh SSSI 488881, 186537 8.2km Northwest

E12 Kingcup Meadows and Oldhouse SSSI 502544, 185219 8.2km Northeast Wood

E13 Great Thrift Wood SSSI 487346, 178447 8.5km Southwest

E14 South West London Waterbodies Ramsar 502302, 175599 8.5km Southeast

E15 Wraysbury and Hythe End Gravel Pits SSSI 500720, 174113 9.1km South

E16 Chawridge Bourne SSSI 489406, 174090 9.4km Southwest

E17 Bisham Woods and Chiltern SSSI, SAC 486474, 185335 9.6km Northwest Beechwoods

E18 Old Rectory Meadows SSSI 503056, 187358 9.8km Northeast

E19 Haymill Valley LNR 494316, 181657 840m West

E20 Cocksherd Wood LNR 494550, 182824 1.4km Northwest

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Figure 3.1: Location of Sensitive Human Health Receptors

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U FOLLOWING AECOM'S EXPRESS AGREEMENT TO SUCH USE, AND ONLY FOR THE \ a i PURPOSES FOR WHICH IT WAS PREPARED AND PROVIDED. m e \ AECOM m o One Trinity Gardens c . t Quayside e n Newcastle upon Tyne m o E16 E15 NE1 2HF c e T +44 (0)191 224 6500 a (! . (! www.aecom.com u e \ \ : Drawing Ref Rev e 0 1 2 3 4 5 m a N e l km FIGURE 3.2 i ± F Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

3.4 Meteorology The dispersion of emissions from a point source is largely dependent on atmospheric stability and turbulent mixing in the atmosphere, which in turn are dependent on wind speed and direction, ambient temperature, cloud cover and the friction created by buildings and local terrain.

Actual measured hourly-sequential meteorological data is available for input into dispersion models, and it is important to select data as representative as possible for the site that is modelled. This is usually achieved by selecting a meteorological station as close to the site as possible, although other stations may be used if the local terrain and conditions vary considerably, or if the station does not provide sufficient data.

The meteorological site used in the 2014 Permit Variation assessment was Heathrow Airport, located approximately 9km southeast of the Multifuel facility, in flat terrain. The 2014 Permit Variation assessment used meteorological data for 2008 – 2013, with 2008 typically providing the worst-case results. AECOM now holds data for the years 2014 – 2018 and therefore the reassessment for this variation application has initially used the original 2008 data for direct comparison to the 2014 Permit Variation results and then also used the more recent years of meteorological data, with results reported for the worst-case meteorological year modelled.

The wind-roses for Heathrow Airport meteorological data are shown in Figure 3.3.

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Figure 3.3: Wind-roses for Heathrow Airport 2008 2014

0° 350° 0° 10° 350° 10° 340° 20° 340° 600 20° 800 330° 30° 330° 30° 320° 500 40° 320° 40° 600 310° 50° 310° 50° 400 300° 60° 300° 60° 300 400 290° 70° 290° 70° 200

200 280° 100 80° 280° 80°

270° 90° 270° 90° 260° 100° 260° 100° 250° 110° 250° 110° 240° 120° 240° 120° 230° 130° 230° 130° 220° 140° 220° 140° 210° 150° 200° 160° 210° 150° 190° 180° 170° 200° 160° 0 3 6 10 16 (knots) 190° 180° 170°

2015 2016

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2017 2018

350° 0° 10° 350° 0° 10° 340° 20° 340° 800 20° 500 330° 30° 330° 30° 320° 40° 320° 40° 400 600 310° 50° 310° 50° 300 300° 60° 300° 60° 400 200 290° 70° 290° 70°

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0 3 6 10 16 (knots) Wind speed 0 1.5 3.1 5.1 8.2 (m/s)

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3.5 Building and Terrain Effects As discussed above, another variable that can have a significant effect on the dispersion of emissions from sources is the presence of buildings or structures near to the emissions points. The wind field can become entrained into the wake of buildings, which causes the wind to be directed to ground level more rapidly than in the absence of a building. If an emission is entrained into this deviated wind field, this can give rise to elevated ground-level concentrations. Building effects are typically considered where a structure of height greater than 40% of the stack height is situated within 8 to 10 stack heights of the emissions source.

The buildings associated with the Multifuel facility which are considered to be of sufficient height and massing to potentially impact on the dispersion of emissions from the release points have included in the model. The building parameters used in the model are shown in Table 3.3, and a visualisation of the buildings is shown in Figure 3.4.

Table 3.3: Modelled Building Parameters

Length Building Location (x, y) Height (m) Width (m) Angle1 (m) Boiler Hall 495311, 181444 48 50 45 107⁰ Cooling Tower 7 495379, 181548 48.8 40 -2 ⁰ Cooling Tower 8 495432, 181534 48.9 40 -2 ⁰ 1 Angle of building length to vertical north. 2 The cooling towers have been modelled as circular structures of 40m diameter and therefore have no designated ‘width’ or ‘angle’.

Figure 3.4: Model Building Visualisation

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The ADMS model is capable of including topographical data, if required. There are two parameters (surface roughness and terrain) which can be employed in the model to describe local topography.

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Surface roughness describes the degree of ground turbulence caused by the passage of winds across surface structures. Ground turbulence is greater in urban areas than in rural areas, for example, due to the presence of tall buildings.

The installation is situated to the west of Slough town centre in an industrial trading estate with residential developments approximately 200m to the north, 500m to the northeast and 1km to the east of the site. A surface roughness of 0.5m, which is representative of parkland and open suburbia, has been selected to represent the local area.

The presence of elevated or complex terrain in the vicinity of the source can also affect the flow pattern of the wind field and therefore the dispersion of emissions. A gradient of 1:10 or greater is normally taken as the criteria for inclusion of terrain in a modelling assessment. The terrain in the vicinity of the installation can be considered to be relatively flat, with no steep gradients or pronounced changes in height and therefore no terrain data has been included within the model.

Predicted Results

The results presented in the 2014 Permit Variation were the worst-case of the single or twin line modelling carried out at that time, based on 2008 meteorological data. Typically, the worst-case results were for the single line operating configuration, due to the lower stack height that had been assumed for this plant. The 2014 Permit Variation results are shown in Table 4.1, together with the results for the proposed HZI twin line plant, at both the NCV design fuel (12.06MJ/kg) and the increased RDF throughput and lower NCV fuel (10.5MJ/kg).

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Table 4.1: Comparison of the 2014 Permit Variation Results and the Proposed Plant (based on 2008 meteorological data)

Reported in 2014 Proposed Plant Proposed Plant Comparison Between the Env Std Permit Variation Design Fuel Lower NCV Fuel PC/NAQS % for the Pollutant Measured as (mg/m3) PC PC/NAQS PC PC/NAQS PC PC/NAQS 2014 Results and (mg/m3) % (mg/m3) % (mg/m3) % the 2020 Low NCV Fuel Results Annual average 40 1.6 4.1% 1.00 2.5% 1.00 2.5% -1.6%

Hourly mean (99.8th percentile) 200 18.3 9.2% 14.2 7.1% 14.0 7.0% -2.2% Nitrogen oxides Annual average at worst case habitat site (as NO2) 30 0.3 0.9% 0.3 0.9% 0.3 0.9% 0.0% (Stoke Common) 24-hr mean (100th percentile) at worst case habitat site 75 5.6 7.5% 2.4 3.2% 2.4 2.4% -5.1% (Burnham Beeches) 24-hour mean (99.18th percentile) 125 16.5 13.2% 10.1 8.1% 10.0 8.0% -5.2%

Hourly mean (99.73th percentile) 350 25.8 7.4% 20.1 5.7% 19.9 5.7% -1.7% Sulphur dioxide (SO2) 15-min mean (99.9th percentile) 266 28.9 10.9% 22.6 8.5% 22.8 8.6% -2.3%

Annual average at worst case habitat site 20 0.07 0.3% 0.07 0.3% 0.07 0.3% 0.0%

Annual average 40 0.11 0.3% 0.07 0.2% 0.07 0.2% -0.1% Particulates (PM10) 24-hour mean (90.41th percentile) 50 1.2 2.4% 0.74 1.5% 0.73 1.5% -0.9%

Particulates (PM2.5) Annual average 20 0.11 0.6% 0.07 0.4% 0.07 0.4% -0.2%

Carbon Monoxide (CO) 8 hour running mean 10,000 15.6 0.2% 13.7 0.1% 13.6 0.1% -0.1%

Annual average 180 0.07 0.0% 0.04 0.0% 0.04 0.0% 0.0%

Ammonia (NH3) Maximum hourly mean 2,500 0.9 0.0% 0.7 0.0% 0.7 0.0% 0.0%

Annual average at worst case habitat site 3 0.007 0.2% 0.007 0.2% 0.007 0.2% 0.0%

VOCs Annual average 5 0.12 2.3% 0.07 1.4% 0.07 1.4% -0.9% Hydrogen chloride Hourly mean (100th percentile) 750 10.3 1.4% 8.0 1.1% 8.0 1.1% -0.3% (HCl) Annual average 16 0.01 0.1% 0.01 0.1% 0.01 0.1% 0.0%

Hydrogen fluoride (HF) Hourly mean (100th percentile) 160 0.7 0.4% 0.5 0.3% 0.5 0.3% -0.1% Daily mean at worst case habitat site 5 0.001 0.0% 0.001 0.0% 0.001 0.0% 0.0%

Annual average 0.25 0.0006 0.2% 0.0004 0.2% 0.0004 0.2% 0.0% Mercury Hourly mean (100th percentile) 7.5 0.009 0.1% 0.007 0.1% 0.007 0.1% 0.0%

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Reported in 2014 Proposed Plant Proposed Plant Comparison Between the Env Std Permit Variation Design Fuel Lower NCV Fuel PC/NAQS % for the Pollutant Measured as (mg/m3) PC PC/NAQS PC PC/NAQS PC PC/NAQS 2014 Results and (mg/m3) % (mg/m3) % (mg/m3) % the 2020 Low NCV Fuel Results Cadmium and Thallium Annual average 0.005 0.0006 11.7% 0.0004 8.0% 0.0004 8.8% -2.9%

Annual average 0.15 0.006 3.9% 0.004 2.7% 0.004 2.7% -1.2% Other metals Hourly mean (100th percentile) 1 0.09 8.7% 0.07 7% 0.07 7% -1.7%

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It can be seen in Table 4.1 that the predicted process contributions associated with the proposed HZI twin line plant, with the design fuel and with the increased throughput of low NCV RDF, result in lower impacts than were reported in the 2014 Permit Variation assessment. It has also been determined that the increased throughput resulting from the lower NCV fuel would result in similar environmental impacts to that determined for the design fuel and thus will not lead to a worsening of the environmental impacts associated with the permitted Multifuel facility.

In addition to the assessment reported in Table 4.1, the emission parameters for the proposed HZI twin line plant have also been modelled with updated meteorological data for Heathrow Airport meteorological site (2014 – 2018), and these results are shown in Table 4.2.

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Table 4.2: Comparison of the 2014 Permit Variation Results and the Proposed Plant (worst case new meteorological data 2014 - 2018)

Reported in 2014 Proposed Plant Lower Comparison Between the NAQS or EAL Permit Variation NCV Fuel PC/NAQS % for the 2014 Pollutant Measured as 3 (mg/m ) PC PC/NAQS PC PC/NAQS Results and the 2020 Low (mg/m3) % (mg/m3) % NCV Fuel Results Annual average 40 1.6 4.1% 1.1 2.7% -1.4%

Annual average at AQMA 40 0.3 0.7% 0.2 0.5% -0.2% Nitrogen oxides Hourly mean (99.8th percentile) 200 18.3 9.2% 14.2 7.1% -2.1% (as NO2) Annual average at worst case habitat site (Stoke Common) 30 0.3 0.9% 0.4 1.2% 0.3% 24-hr mean (100th percentile) at worst case habitat site 75 5.6 7.5% 3.6 4.8% -2.7% (Burnham Beeches) 24-hour mean (99.18th percentile) 125 16.5 13.2% 11.4 9.1% -4.1% Hourly mean (99.73th percentile) 350 25.8 7.4% 20.1 5.7% -1.7% Sulphur dioxide (SO2) 15-min mean (99.9th percentile) 266 28.9 10.9% 22.9 8.6% -2.3%

Annual average at worst case habitat site (Stoke Common) 20 0.07 0.3% 0.09 0.5% 0.2%

Annual average 40 0.11 0.3% 0.08 0.2% -0.1% Particulates (PM10) 24-hour mean (90.41th percentile) 50 1.2 2.4% 0.76 1.5% -0.9%

Particulates (PM2.5) Annual average 20 0.11 0.6% 0.08 0.4% -0.2%

Carbon Monoxide (CO) 8 hour running mean 10,000 15.6 0.2% 14.3 0.1% -0.1%

Annual average 180 0.07 0.0% 0.04 0.0% 0.0%

Ammonia (NH3) Maximum hourly mean 2,500 0.9 0.0% 0.7 0.0% 0.0%

Annual average at worst case habitat site (Stoke Common 3 0.007 0.2% 0.009 0.3% 0.1%

VOCs Annual average 5 0.12 2.3% 0.08 1.6% -0.7%

Hydrogen chloride (HCl) Hourly mean (100th percentile) 750 10.3 1.4% 8.6 1.1% -0.3%

Annual average 16 0.01 0.1% 0.01 0.0% 0.0%

Hydrogen fluoride (HF) Hourly mean (100th percentile) 160 0.7 0.4% 0.5 0.3% 0.0%

Daily mean at worst case habitat site (Stoke Common) 5 0.002 0.0% 0.002 0.0% 0.0%

Annual average 0.25 0.0006 0.2% 0.0004 0.2% 0.0% Mercury Hourly mean (100th percentile) 7.5 0.009 0.1% 0.007 0.1% 0.0%

Prepared for: Slough Heat and Power Limited AECOM 20 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Reported in 2014 Proposed Plant Lower Comparison Between the NAQS or EAL Permit Variation NCV Fuel PC/NAQS % for the 2014 Pollutant Measured as 3 (mg/m ) PC PC/NAQS PC PC/NAQS Results and the 2020 Low (mg/m3) % (mg/m3) % NCV Fuel Results Cadmium and Thallium Annual average 0.005 0.0006 11.7% 0.0004 7.7% -4.0%

Annual average 0.15 0.006 3.9% 0.004 2.6% -1.3% Other metals Hourly mean (100th percentile) 1 0.09 8.7% 0.07 6.7% -2.1%

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It can be seen in Table 4.2 that the predicted process contributions associated with the proposed HZI twin line plant, using the more recent meteorological data, still results in impacts than are either lower or the same as the results that were reported in the 2014 Permit Variation assessment for all human health receptors, and therefore the associated impacts with the change in fuel throughout and NCV remain less than those reported for the 2014 Permit Variation assessment.

As this has been shown to be the case for the pollutant species included in this assessment, it has not been considered necessary to revise the dioxin, furan and PCB assessment, nor the Human Health Risk Assessment submitted with the 2014 Permit Variation, as again, the new impacts would be lower than those predicted at that time, and have already been deemed acceptable by the Environment Agency. There have been no other changes to the methodologies of these assessments, or to the sensitive receptors identified that would affect the results presented at that time.

The annual average impacts of NOx and SO2 at the worst case ecological site (Stoke Common) show a slight increase over the results reported in the 2014 Variation with the more recent meteorological data. This was not shown to be the case with the results for the Proposed Plant at the design fuel or the lower NCV fuel presented in Table 4.1, using the original 2008 meteorological data. It is therefore considered that the slight increase shown in Table 4.2 is due to the meteorological data used, rather than as a result of the change in the release parameters associated with the Lower NCV fuel. The 2014 Variation results were based on the worst-case meteorological year of 2008, whereas the year resulting in the worst-case impacts with the new meteorological data is 2014. Comparing the wind roses provided in Figure 3.3 clearly shows that the 2014 data has a much greater south westerly influence than the 2008 data, therefore resulting in the higher PC at Stoke Common, which is to the northwest of the Multifuel facility. In addition, the meteorological data for the years 2015 – 2018 inclusive all result in PCs at the Stoke Common receptor that are less than 0.28µg/m3 or 0.9% of the Critical Level, and therefore would be the same or less than that reported in the 2014 Permit Variation, indicating that the result for the 2014 is an anomaly.

For completion, the new modelling results for the lower NCV fuel, and the updated meteorological data, have been presented in Table 4.3 in full, with consideration of the revised background concentrations and inclusion of the PECs. In addition, Table 4.4 shows the full results at all the identified habitat receptors with the new meteorological data.

Prepared for: Slough Heat and Power Limited AECOM 22 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Table 4.3: Model Results for the Proposed Plant at the Lower NCV Fuel – Human Health Impacts (worst case new meteorological data 2014 - 2018)

PC PC/NAQS BC PEC/NAQS Pollutant Measured as NAQS or EAL (mg/m3) Insignificant? (mg/m3) % (mg/m3) %

No PEC >70% at the maximum Max annual average 40 1.1 2.7% 31.0 80% location offsite, due to high background concentration. Nitrogen oxides (as NO2) Annual average at AQMA 40 0.2 0.5% 31.0 78% Yes PC <1%.

Hourly mean (99.8th percentile) 200 14.2 7.1% 62.0 38% Yes PC <10%.

24-hour mean (99.18th percentile) 125 11.4 9.1% 7.8 15% Yes PC <10%.

th Sulphur dioxide (SO2) Hourly mean (99.73 percentile) 350 20.1 5.7% 7.8 8% Yes PC <10%. 15-min mean (99.9th percentile) 266 22.9 8.6% 7.8 12% Yes PC <10%.

Annual average 40 0.08 0.2% 16.9 42% Yes PC <1%. Particulates (PM10) 24-hour mean (90.41th percentile) 50 0.8 1.5% 33.8 69% Yes PC <10%.

Particulates (PM2.5) Annual average 20 0.08 0.4% 11.3 57% Yes PC <1%.

8 hour running mean 10,000 14.3 0.1% 392 4% Yes PC <10%. Carbon Monoxide (CO) Hourly mean (100th percentile) 30,000 21.5 0.1% 392 1% Yes PC <10%.

Annual average 180 0.04 0.0% 1.8 1% Yes PC <1%. Ammonia (NH3) Maximum hourly mean 2,500 0.7 0.0% 3.9 0.2% Yes PC <10%.

VOCs Annual average 5 0.08 1.6% 0.51 12% Yes PEC <70%. Hydrogen chloride Hourly mean (100th percentile) 750 8.6 1.1% 0.7 1% Yes PC <10%. (HCl) Annual average 16 0.01 0.1% 0.003 0.1% Yes PC <1%. Hydrogen fluoride (HF) Hourly mean (100th percentile) 160 0.5 0.3% 0.006 0.3% Yes PC <10%.

Annual average 0.25 0.0004 0.2% 0.002 1% Yes PC <1%. Mercury Hourly mean (100th percentile) 7.5 0.007 0.1% 0.004 0.1% Yes PC <10%.

Cadmium and Thallium Annual average 0.005 0.0004 7.7% 0.0002 11% Yes PEC <70%.

Annual average 0.15 0.004 2.6% 0.02 16% Yes PEC <70%. Other metals Yes PC / NAQS – twice the Hourly mean (100th percentile) 1 0.07 6.7% 0.001 7% annual average BC <20%.

Prepared for: Slough Heat and Power Limited AECOM 23 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Table 4.3 shows that all impacts can be screened as either insignificant or not significant except for annual average NO2. This is largely due to the high background concentration that has been used in the assessment, taken from the Salt Hill automatic monitoring station. The monitoring station is close to AQMA3, and therefore its location has been selected to measure the elevated concentrations expected in the AQMAs vicinity, and therefore it is considered likely that the background concentrations in the vicinity of the closest receptors to the Multifuel facility (and therefore the most affected receptors) would be below this value.

As stated previously, the impacts predicted in this assessment, and also the background concentrations used are actually lower than the 2014 Permit Variation assessment.

Isopleth figures of the annual average and hourly NO2 concentrations are provided in Annex B.

Prepared for: Slough Heat and Power Limited AECOM 24 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Table 4.4: Model Results for the New Proposed Plant at the Lower NCV Fuel – Ecological Impacts (worst case new meteorological data 2014 - 2018)

Annual Average NOx Impacts Daily Average NOx Impacts Annual Average NH3 Impacts Daily Average HF Impacts

Receptor CL PC PC/CL CL PC PC/CL CL PC PC/CL CL PC PC/CL (mg/m3) (mg/m3) % (mg/m3) (mg/m3) % (mg/m3) (mg/m3) % (mg/m3) (mg/m3) %

E1 Burnham Beeches 0.28 0.9% 3.56 4.7% 0.007 0.7% 0.0015 0.0% E2 Stoke Common 0.35 1.2% 2.03 2.7% 0.009 0.9% 0.0018 0.0% E3 South Lodge Pit 0.11 0.4% 1.83 2.4% 0.003 0.3% 0.0006 0.0% E4 Bray Pennyroyal Field 0.14 0.5% 2.40 3.2% 0.003 0.3% 0.0007 0.0% E5 Littleworth Common 0.13 0.4% 3.55 4.7% 0.003 0.3% 0.0007 0.0% E6 Bray Meadows 0.08 0.3% 1.91 2.5% 0.002 0.2% 0.0004 0.0% E7 Windsor Forest and Great Park 0.07 0.2% 1.45 1.9% 0.002 0.2% 0.0003 0.0% E8 Black Park 0.18 0.6% 1.22 1.6% 0.005 0.5% 0.0009 0.0% E9 Cannoncourt Farm Pit 0.06 0.2% 0.96 1.3% 0.001 0.1% 0.0003 0.0% E10 Wraysbury No. 1 Gravel Pit 0.05 0.2% 0.91 1.2% 0.002 0.2% 0.0003 0.0% 30 75 1 5 E11 Cock Marsh 0.05 0.2% 1.34 1.8% 0.001 0.1% 0.0003 0.0% E12 Kingcup Meadows and Oldhouse Wood 0.12 0.4% 0.81 1.1% 0.003 0.3% 0.0006 0.0% E13 Great Thrift Wood 0.06 0.2% 1.02 1.4% 0.001 0.1% 0.0003 0.0% E14 South West London Waterbodies 0.07 0.2% 1.04 1.4% 0.002 0.2% 0.0003 0.0% E15 Wraysbury and Hythe End Gravel Pits 0.05 0.2% 0.83 1.1% 0.000 0.0% 0.0003 0.0% E16 Chawridge Bourne 0.10 0.3% 1.24 1.7% 0.002 0.2% 0.0005 0.0% E17 Bisham Woods and Chiltern 0.04 0.1% 0.81 1.1% 0.001 0.1% 0.0002 0.0% Beechwoods E18 Old Rectory Meadows 0.10 0.3% 0.80 1.1% 0.003 0.3% 0.0005 0.0% E19 Haymill Valley 0.28 0.9% 6.38 8.5% 0.007 0.7% 0.0015 0.0% E20 Cocksherd Wood 0.34 1.1% 5.63 7.5% 0.009 0.9% 0.0018 0.0%

Prepared for: Slough Heat and Power Limited AECOM 25 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

It can be seen from Table 4.4 that the annual average results at all the ecological receptors are below the threshold for insignificance (1%) for nearly all the identified sites, for all pollutant species assessed. Where the PC is over the threshold of insignificance, it is only by 0.1% - 0.2% (and for NOx only), and therefore only slightly over the threshold. As stated previously it is considered that this is due to the impacts of the new meteorological data however, rather than due to the change in fuel specification, as the results presented in Table 4.1, comparing the two fuel types at the Stoke Common receptor using the original 2008 meteorological data are identical. In addition, the results obtained with meteorological years 2015 – 2018 inclusive predict results that are less than 0.9% of the Critical Level and therefore the same as the 2014 Variation assessment.

The annual average impacts of ammonia have also been assessed against the more stringent critical level for lichens and bryophytes and still can be deemed insignificant at all sites.

The daily NOx impacts are all less than the 10% threshold for insignificance at all sites.

It is therefore considered that the predicted impacts from the operational Multifuel facility would not lead to any exceedance of the Critical Levels at any of the identified habitat sites.

In the 2014 Variation assessment, the only ecological site that experienced deposition nutrient nitrogen impacts that were over the 1% screening threshold was Burnham Beeches. No sites were predicted to experience acid depositional impacts that were over the 1% screening threshold.

As such, the N-depositional results for Burnham Beeches for the 2014 Variation and this revised assessment, with the new meteorological data, have therefore provided in Table 4.5.

Table 4.5: N-Deposition Impacts Compared for the 2014 Variation (2008 meteorological data) and the Revised Assessment (worst case new meteorological data 2014 - 2018)

Dry Deposition Nitrogen Critical Background Predicted Predicted Increase Assessment Critical Load N-Deposition Increase in N- as % of Critical Load Class kg N/ha/yr kg N/ha/yr Deposition Load kg N/ha/yr Coniferous 2014 Variation 5-15 33.2 0.10 2.1% Woodland New Proposed Plant Lower NCV Fagus 10-20 25.6 0.06 0.7% Fuel (new met Woodland data)

The Burnham Beeches site details on the APIS website now no longer lists Coniferous Woodland as being present, and therefore the habitat type with the lowest Critical Load range now listed is Fagus Woodland, which has a higher Critical Load range than Coniferous Woodland. As such, the pre- dicted impacts at the site are not only lower in terms of the predicted kg N-Deposition/ha/yr, showing a reduction in the impacts over the 2014 Variation assessment, but also in the %age of the Critical Load it represents. The impacts have therefore reduced from 2.1% of the Critical Load to 0.7% which would now be considered to be insignificant.

Conclusions

AECOM has carried out a revised dispersion modelling assessment to determine the potential environmental impacts on Air Quality of an increase in fuel throughput that would arise when using lower Net Calorific Value (NCV) for the Multifuel facility at the Slough Heat and Power Site.

The assessment has compared the emission parameters originally assessed for the 2014 Permit Variation against revised parameters provided for the plant that is now proposed to be installed. The updated design parameters result in a higher normalised flue gas flow rate, with higher mass emission

Prepared for: Slough Heat and Power Limited AECOM 26 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005 rates (at the ELV) than those previously assessed, for both the design fuel (12.06 MJ/kg) and the lower NCV fuel (10.5 MJ/kg). However, the proposed plant now has a higher stack release temperature and smaller stack diameter (resulting in a higher efflux velocity) than that assessed in the 2014 Permit Variation. This results in improved thermal and momentive buoyancy of the stack emissions.

Detailed dispersion modelling carried out of the emissions from the now proposed plant shows that the impacts at human health receptors are lower than those detailed in the 2014 Permit Variation for both the design fuel and the lower NCV fuel, both using the original 2008 meteorological data and with more recent meteorological data. There is also no discernible difference in the impact on Air Quality between the design fuel and the low NCV fuel. Therefore, it is considered that human health impacts will improve from those presented in the 2014 Permit Variation as a result of the now proposed facility.

Annual average impacts at the worst-case ecological site for annual average impacts (Stoke Common SSSI) are the same as those presented in the 2014 Permit Variation when using the original 2008 meteorological data, however the more recent meteorological data shows a slight increase in impacts for just one of the five years modelled (2014). That said, the predicted concentration for the worst-case meteorological year of 2014 is only 0.2% over the 1% threshold for insignificance and therefore is unlikely to result in significant impacts at this site. It is considered that this is a phenomenon of the meteorological data used in the assessment, rather than being due to the different emission parameters resulting from the change in fuel NCV. Depositional impacts (for Nitrogen) at the Burnham Beeches (SAC) receptor have reduced from those presented in the 2014 Permit Variation from 2.1% of the lower Critical Load to less than 1%, and are therefore insignificant. It has therefore been determined that there is no impact on Air Quality from operating the Multifuel facility on a lower NCV fuel, thus demonstrating that an increase to the annual fuel limit for the Multifuel Plant from 438,000 to 480,000 tonnes per annum has no adverse environmental impact. This updated Air Quality Assessment has, using the design parameters for the proposed twin line plant, also determined that the impacts on Air Quality are in line with, or lower than, those presented in the 2014 Permit Variation.

Prepared for: Slough Heat and Power Limited AECOM 27 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Annexes

Prepared for: Slough Heat and Power Limited AECOM 28 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Annex A – Sensitivity Assessment

Sensitivity to the model results to the new meteorological data used for this assessment has been carried out, to determine the effect that this has on the maximum NO2 model outputs. The maximum short term predicted concentration came from the 2014 met year, whereas the maximum annual average result was associated with the 2017 met year. The short term results varied by -1% from the results reported for the met year that returned the lowest result and the annual average impacts varied by -45%. It is therefore considered that the results reported in the assessment above are conservative and that on an average year, the predicted impacts will be lower than reported in the assessment carried out.

Prepared for: Slough Heat and Power Limited AECOM 29 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Annex B – Isopleth Figures

3 Isopleths of Annual Average NO2 Concentrations (µg/m ) from the Multifuel Facility (Lower NCV Fuel)

Ordnance Survey © Crown Copyright 2020. All rights reserved. Licence number 100022432

Prepared for: Slough Heat and Power Limited AECOM 30 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

3 th Isopleths of Hourly Average NO2 Concentrations (µg/m ) (as the 99.79 percentile) from the Multifuel Facility (Lower NCV Fuel)

Ordnance Survey © Crown Copyright 2020. All rights reserved. Licence number 100022432

Prepared for: Slough Heat and Power Limited AECOM 31 Appendix B - Air Quality Assessment Project reference: 60578218 Project number: 60578218.005

Prepared for: Slough Heat and Power Limited AECOM 32 Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Appendix C – List of Company Directors

Company Name: Slough Heat & Power Limited

Company number: 00174142

Registered office address: No.1 Forbury Place, 43 Forbury Road, Reading, United Kingdom, RG1 3JH

Date of Incorporation: 9 April 1921

List of Active Directors (as per Companies House)

Director Name Date of Birth Appointed on (Last name, First name) Hayward, Mark Richard November 1963 29 March 2013 Mullen, John November 1972 1 January 2018

Prepared for: Slough Heat and Power Limited AECOM Environmental Permit Variation Application Project reference: 60578218 Project number: 60578218.005

Appendix D – Application Checklist

Part F1 – Q6

Question reference Document title Document reference Part A, Q5c; List of active Company Appendix C, 60578218-ACM-PM-RP-EN-001-A Part A, Appendix 1, Q4 Directors Part C2, Q2b, Table 1; Proposed Variation Section 2.2, 60578218-ACM-PM-RP-EN-001-A Part C3, Q1 Part C2, Q3d Management System Section 4.7, 60578218-ACM-PM-RP-EN-001-A Part C2, Q5a Site Layout Plan Fig 1, App A, 60578218-ACM-PM-RP-EN-001-A Part C2, Q5c Non-Technical Summary Non-Technical Summary, 60578218-ACM-PM-RP-EN-001-A Part C2, Q6 Environmental Risk Section 7, 60578218-ACM-PM-RP-EN-001-A Assessment Part C3, Q2 Emissions to air Section 5.1, 60578218-ACM-PM-RP-EN-001-A Part C3, Q2 Emissions to water Section 5.2, 60578218-ACM-PM-RP-EN-001-A Part C3, Q2 Emissions to sewer Section 5.3, 60578218-ACM-PM-RP-EN-001-A Part C3, Q2 Emissions to land Section 5.4, 60578218-ACM-PM-RP-EN-001-A Part C3, Q3a Technical Standards Section 4.1, 60578218-ACM-PM-RP-EN-001-A Part C3, Q3c, Q6d Raw materials Section 4.3, 60578218-ACM-PM-RP-EN-001-A Part C3, Q4a Monitoring Section 6, 60578218-ACM-PM-RP-EN-001-A Part C3, Q4b Monitoring emissions to air Section 6.2, 60578218-ACM-PM-RP-EN-001-A Part C3, Q6a Energy efficiency Section 4.5, 60578218-ACM-PM-RP-EN-001-A Part C3, Q6e Waste Section 4.4, 60578218-ACM-PM-RP-EN-001-A

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